Determination of point of zero charge of natural organic materials

Multi-Analytical Approach for the Acid-Base, Thermal and Surface Properties Assessment of Waste Biomasses

A multi-analytical approach was used to comprehensively characterize the acid-base, thermal, and surface properties of agri-food processing wastes (i.e., original and pre-treated bergamot, grape and olive pomaces). These biomasses, often underutilised and inadequately studied in terms of their physicochemical properties, were investigated under varying ionic strength conditions at t = 25 °C. This investigation uniquely integrates multiple advanced techniques: Brunauer-Emmett-Teller porosimetry, Scanning Electron Microscopy, Thermogravimetric Analysis coupled with Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, Attenuated Total Reflectance Fourier-Transform Infrared, and potentiometry to provide a holistic understanding of these biomasses potential for environmental remediation. The modelling of ionic strength-dependent acid-base behaviour, established using an extended Debye-Hückel-type equation, revealed the dominant role of carboxylic groups as active sites across all pomace types, although with variations in abundances across the different samples. Additionally, morphological analysis highlighted the presence of irregularly shaped particles, heterogeneous size distributions, and distinct thermal stability trends, with grape pomace exhibiting the highest mass loss. These findings underscore the significant potential of these biomasses for the remediation of cationic pollutants from natural waters. Moreover, this comprehensive characterisation not only advances the understanding of agri-food waste valorisation but also provides a robust framework for designing targeted strategies in environmental applications.

New insights into thallium(I) behaviors at birnessite surfaces: Effects of an organic buffer and goethite

Understanding the environmental behavior of thallium (Tl) is crucial due to its high toxicity and increasing anthropogenic presence. This study investigated the adsorption and redox behaviors of Tl(I) with acid birnessite (AcBi) in the presence of 1,4-piperazine-diethanesulfonic acid (PIPES) and goethite under diffusion-limited conditions using Donnan reactors in aerobic and anaerobic environments. Our findings indicate that Tl(I) preferentially adsorbs onto AcBi, with capacities 20 to 100 times higher than onto goethite, even when AcBi is partial reduced by PIPES. No net Tl(I) oxidation occurred in the Donnan reactors, likely due to complex electron transfer processes between Tl(I), birnessite, and PIPES. Any Tl(III) generated from Tl(I) oxidation by birnessite was rapidly reduced back to Tl(I) by PIPES. This was confirmed in batch experiments where reduced Tl(III) on birnessite surfaces and in Tl(III) salts. These findings highlight the need to assess the impact of Good's buffers on redox reactions involving manganese oxides and Tl, while also providing insights into the competitive retention of Tl on manganese and iron (hydr)oxides, with implications for Tl mobility and bioavailability in natural environments.

Characterization and adsorption performance of nano-hydroxyapatite synthesized from Conus litteratus waste seashells for Congo red dye removal

In this research, nano-hydroxyapatite synthesized from Conus litteratus seashells (Ss/nHAp) and the potential of Ss/nHAp as an adsorbent for eliminating Congo Red (CR) dye from aqueous solutions were explored. The synthesized Ss/nHAp was subjected to characterization using various techniques, including XRD, XPS, FTIR, Raman, BET, FESEM etc. in order to understand the material thoroughly. Batch adsorption experiments were conducted to establish the optimal conditions for removing the dye, considering variables such as adsorbent dosage, contact time, pH and initial dye concentration. 85% of the CR dye was eliminated within a short span of 10 minutes using a minimal adsorbent dose of 0.1 g, under neutral pH and room temperature, showcasing its efficiency. The adsorption process adhered to pseudo second order kinetics and was best fitted by the Langmuir isotherm model, with a maximum adsorption capacity (q max) of 24 mg g-1. The material's reusability was demonstrated through regeneration studies, with efficiency slightly decreasing to 74% by the fifth cycle due to adsorbent loss. This study establishes Ss/nHAp as a low-cost, eco-friendly, and effective adsorbent for dye-contaminated water treatment, paving the way for future applications in industrial wastewater remediation.

Insights into the performance and mechanism of a reinforced lignocellulosic sorbent fabricated from sawdust biomass for multi-tasking application in enrofloxacin removal and monitoring

Natural lignocellulose-based materials have numerous strengths such as abundance, cheap price and biodegradability, which indicates a brilliant prospect for environmental protection. This work aimed to design an efficient sorbent (NaSS-PSD) by pine sawdust (PSD) for the surveillance and management of enrofloxacin (ENR). In the study, sodium styrenesulfonate (NaSS) was chosen as an effective monomer to ameliorate the performance of PSD by graft copolymerization. The removal of ENR by NaSS-PSD was enhanced in comparison with the ungrafted ones under investigated conditions. Pseudo-second-order and Temkin were the best-fitted models to describe the adsorption behavior. For the first time, NaSS-PSD was employed as a novel extractant of solid-phase extraction (SPE) and dispersive solid-phase microextraction (DSPME) to develop accurate, eco-friendly and economic analytical techniques for trace ENR determination. Good linearity and reproducibility were obtained. The limits of detection were 0.41 μg/L for DSPME-HPLC-DAD technique and 0.15 μg/L for SPE-HPLC-DAD technique. These two methods exhibited satisfying practicability when applied to quantify ENR residue in real waters. The study on interfacial interaction mechanism and preferential binding sites suggested that hydrogen bond and π-π interactions took the primary responsibility. Our work provides a good perspective for tailoring natural lignocellulosic biomass to be alternative adsorbents for emerging pollutants.

Utilizing green zinc oxide nanoparticles as a sensing platform for ascorbic acid

We prepared zinc oxide nanoparticles (ZnO NPs) via a green synthesis and used them for the fluorescence sensing of ascorbic acid (AA). For obtaining these nanoparticles, we used an extract from Batavia lettuce as a reducing agent for zinc acetate in a simple, fast, and environmentally friendly synthesis. The ZnO NPs were characterized by X-ray diffractometry (XRD), ultraviolet-visible spectroscopy (UV-vis), Fourier Transform Infrared spectroscopy (FTIR), scanning electron microscopy (SEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), photoluminescence, point of zero-charge (pHpzc), and chromaticity studies. We verified that the ZnO NPs had an average diameter of 6 nm, with a wurtzite crystalline structure, and when excited at 320 nm emitted radiation in the blue region. The methodology for AA detection is based on the observed increase in fluorescence of the molecule complex formed on the ZnO NPs surface after 20 min of interaction. The results indicated that the proposed technique of analysis is fast, simple, and highly sensitive, with a detection limit for AA of 5.15 μM. Furthermore, the nanoparticles presented excellent photostability for at least 30 days, and low sensitivity to other biological organic molecules. The green ZnO NPs also exhibited an efficient response to the presence of AA in actual complex samples, suggesting that the platform here proposed can find use in clinical analysis protocols.

Studying the synthesis, antimicrobial activity, and phenol red removal of gelatin-stabilized copper nanoparticles

This study presents a synthesis method for environmentally friendly copper nanoparticles using ascorbic acid and gelatin as key components. The influence of precursor concentration, reductant amount, and stabilizer on the process was systematically investigated to obtain optimal results for the synthesis. The optimal parameters for forming copper nanoparticles, including 20 g per L gelatin, 19.3 mM (AcO)2Cu, and 41.5 mM ascorbic acid, were determined using a central composite design of the response surface methodology. Successful generation of pure copper nanoparticles with both spherical and cylindrical shapes, whose sizes were 43.1 and 105.2 nm, respectively, was confirmed by X-ray diffraction analysis and transmission electron microscopy. The synthesized nanomaterial was stable for a two-week storage time after which they gradually oxidized into Cu2+ ions. During antimicrobial activity testing, the synthesized nanoparticles displayed distinctive ability to inhibit the growth of Gram-positive bacteria (Lactobacillus fermentum, Bacillus subtilis, and Staphylococcus aureus), Gram-negative bacteria (Escherichia coli), and cancer cells (A549, Hep-G2, KB, and MCF7). Copper nanoparticles synthesized by chemical reduction demonstrated notable inhibitory activity against various pathogenic fungi that affect plants, including Fusarium solani, Rhizoctonia solani, and Colletotrichum gloeosporioides. Additionally, the catalytic activity of the produced nanomaterial with a bandgap energy of 2.14 eV and a specific surface area of 40.6 m2 g-1 was explored in the degradation of phenol, a common dye used in laboratories and industries. An optimized phenol red removal of 94.4% was achieved after a 540 second reaction time using response surface methodology, specifically a central composite design with an optimal dosage of copper nanoparticles at 31.5 ppm, a NaBH4 concentration of 53.1 mM, and a pH of 7.5.

Green Synthesis of Fe2O3 Nanoparticles Using Eucalyptus globulus Leaf Extract on Pinus radiata Sawdust for Cationic Dye Adsorption

The present study reports the synthesis of Fe2O3 nanoparticles on Pinus radiata sawdust (Fe2O3@PS) using a Eucalyptus globulus leaf extract. The morphology and structure of Fe2O3@PS were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis diffuse reflectance. The adsorption capacity of the system was evaluated by testing its ability to remove the Rhodamine B (RhB) dye. The optimization of the system was carried out using the Plackett-Burman design (PBD) and the response surface methodology (steepest ascent and the Box-Behnken design), which provided information on the main parameters affecting the adsorption process. The PBD results showed that the most important parameters for the removal of RhB using Fe2O3@PS were the removal time, the RhB concentration, and the initial pH of the system. The reusability of Fe2O3@PS under optimal conditions was tested and it was found to maintain its efficiency after five cycles of use. The efficiency and rate of RhB removal observed at pH values near 7.0 were found to be predominantly influenced by electrostatic interactions. In contrast, the analyses conducted at pH values near 8.3 exhibited reduced influence from electrostatic attractions, with π-π interactions and hydrogen bonds emerging as dominant forces. At pH values exceeding 8.3, all potential interactions between RhB and Fe2O3@PS exhibited diminished strength. This research provides valuable information on the formation of eco-friendly nanoparticles immobilized on a forest residue such as sawdust, which can effectively remove organic pollutants like RhB. This contributes to the valorization of resources and the search for solutions to water pollution.

Unripe Plantain Peel Biohydrogel for Methylene Blue Removal from Aqueous Solution

Dye contamination is a serious environmental issue, particularly affecting water bodies, driving efforts to synthesize adsorbent materials with high dye-removal capacities. In this context, eco-friendly and cost-effective materials derived from bioresidues are being explored to recycle and valorize waste. This study investigates the synthesis, characterization, and application of a biohydrogel made from unripe plantain peel (PP), modified with carboxymethyl groups and crosslinked using varying concentrations of citric acid (CA), an eco-friendly and economical organic acid. The materials were characterized by ATR-FTIR, TGA, and SEM, confirming the successful synthesis of hydrogels, which exhibited rough, irregular surfaces with micropores. Additionally, the materials were analyzed for their pH point of zero charge, swelling capacity, and methylene blue (MB) dye removal efficiency. The results indicate that the biohydrogel formed with 1% CA exhibited the most favorable characteristics for MB removal. Kinetic studies revealed that the adsorption mechanism is pH-dependent, with equilibrium being reached in 720 min. The Freundlich isotherm model provided the best fit for the adsorption data, suggesting a heterogeneous surface and a multilayer adsorption process, with a maximum retention capacity of 600.8 ± 2.1 mg/g at pH 4. These findings contribute to the development of cost-effective and efficient materials for dye removal, particularly from water bodies.

Enhancing verapamil trace determination from biological matrices by bar adsorptive microextraction

Verapamil is an L-type calcium channel blocker widely used in the treatment of cardiovascular diseases such as hypertension, angina and arrhythmias, requiring accurate therapeutic monitoring to maintain plasma, urine and saliva concentrations within a safe range. In this context, a novel analytical approach has been proposed to determine verapamil in biological samples, using bar adsorptive microextraction coated with reversed-phase polymers followed by high-performance liquid chromatography with diode array detection. Two adsorbents have been chosen, i.e. STRATA-CN and ENVI-18 polymers, showing recoveries from 56.01 ± 2.16% to 96.82 ± 0.61% under optimized experimental conditions, such as sample pH: 10.0 (STRATA-CN) and 8.0 (ENVI-18), 2 h of equilibrium time, stirring speed at 990 rpm, back-extraction solvent using methanol:acetonitrile (1 : 1 v/v), and 1 h under sonication. The analytical method showed linearity from 20 to 600 ng mL-1 (r ≥ 0.99), as well as adequate precision (with RSD% below 15%) and accuracy (with RE% within 15% of the nominal value). Finally, the analytical method was applied to plasma, urine and saliva samples and proved to be a promising alternative for the trace analysis of verapamil in biological matrices.

Insights into the adsorption of emerging organic contaminant by low-cost readily separable modified jute fiber

A high-efficiency biosorbent based on the low-priced jute fiber was developed, characterized, and applied to remove the emerging organic contaminant diclofenac from aqueous solutions. Jute fiber was treated by NaOH (named AJF) followed by grafting different amounts of trimethyl[3-(trimethoxysilyl) propyl] ammonium chloride (named AJF-TTSAC). The composition, morphology, porosity, and adsorption features of the neat and modified jute fiber were evaluated and compared. The surface of neat JF was smooth, nonporous, and free of cracks. NaOH treatment increased the fibrillation, created cracks and grooves, and increased the oxygen content, total pore volume, and surface area. In comparison to AJF, grafting TTSAC filled in the crevices, grooves, and spaces between fibrillates, and decreased the total pore volume and surface area. The adsorption of diclofenac by the neat and modified JF occurred at highly acidic pHo and peaked at pHo 3. Among the neat and modified JF, AJF-TTSAC5 was the most efficient followed by AJF. The efficiency of AJF and AJF-TTSAC5 was highest using 1.00 g/L, at 35 °C and was not affected by the presence of NaCl. The Elovich, pseudo-first-order, and pseudo-second-order models described the adsorption kinetic satisfactorily with the marginal advantage of Elovich for AJF and pseudo-second-order for AJF-TTSAC5. The isotherm study exposed the multilayer and physisorption nature of the adsorption of diclofenac onto AJF and AJF-TTSAC5. The Langmuir monolayer saturation capacity of AJF-TTSAC5 was 37.43 mg/g which revealed its great potential relative to other adsorbents in the literature. The AJF and AJF-TTSAC5 were easily regenerated using distilled water and kept good performance for 5 repetitive cycles.

Silylation of phosphorylated cellulosic fibers with an aminosilane

In this work, phosphorylated cellulosic fibers were functionalized with an aminosilane ((3-aminopropyl)triethoxysilane, APTES) using a simple and economical method. Several characterization were performed to determine the types of bonds between phosphorylated fibers and grafted APTES. The thermal behavior, hydrophobicity and surface charge variation as a function of pH of the multifunctional cellulose fibers were determined. Results demonstrate that APTES should proceed through Si-O-C, and possibly Si-O-P, covalent bonds with cellulose although the dimerization of silane through Si-O-Si bonds has also been observed. The terminal amino groups are expected to be partially involved in hydrogen bonds with phosphate hydroxyl groups found at phosphorylated cellulose fiber surface, causing a pulling in the configuration of the grafted APTES. The two chemical modifications proposed in this work do not significantly modify the morphology of cellulose fibers. XRD analysis also shows that the crystal structure of the phosphorylated fibers did not change after functionalization with APTES. The silylated phosphorylated fibers show potential flame-retardant properties with improved hydrophobicity. Furthermore, the functionalization of phosphorylated fibers with APTES changes the pH of zero charge point from 3.2 to 9.4 and providing a zwitterionic structure suitable for the simultaneous adsorption of both cationic and anionic species.

Utilizing industrial wastewater sludge-derived biochar for enhancing strength and microstructure of soft soil- An infrastructure application of wastewater sludge

This study proposes a waste-to-value approach; specifically focusing on the utilization of industrial wastewater sludge (IWS) derived pyrolytic biochar (PBC) as an alternative to conventional carbon positive soil stabilizing materials. The IWS was subjected to thermogravimetric analysis (TGA) in N2 environment which suggested the pyrolysis temperature of 450 °C for the synthesis of PBC. Five different dosages of PBC by weight were mixed with the soft soil (SS) and unconfined compressive strength (UCS) values were examined across the various curing periods. Test results confirmed that UCS and stiffness values of soil-PBC matrix increased 4-5 and 5-6 times to that of virgin soil respectively. The PBC increased the cation exchange capacity (CEC), point of zero charge (pHpzc), alkalinity, and water holding capacity of the soil thereby assisted to initiate pozzolanic reactions. Various spectroscopic techniques were performed to investigate the strength development mechanism. Free oxide of calcium (CaO) in PBC disturbed the laminated structure of soil, reacted with oxides of silica (SiO2) and other silicates of aluminum thereby densifying the soil-PBC structure. Further, leaching test was performed on soil-PBC matrices to evaluate the environmental viability of the PBC. The statistical significance of the test results was confirmed using the Analysis of Variance (ANOVA) technique. Overall, this study concludes that PBC has the potential to serve as an environmentally friendly alternative to conventional soil stabilizing materials.

Removal of persistent and mobile organic micropollutants from drinking water utilizing a synthesized waste-derived adsorbent

Persistent and mobile (PM) substances refer to a wide range of organic micropollutants (OMPs) with high persistence and mobility in water. So far, only a few methods have been explored for the removal of PM substances from drinking water. In this work, a new adsorbent based on spent coffee grounds and aluminum waste was synthesized and utilized to remove 25 OMPs, including 22 PM substances, from drinking water. Different characterization methods, including powder X-ray diffraction (XRD), analyses according to Brunauer-Emmett-Teller (BET), field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS), were applied to describe the adsorbent's textural and structural characteristics. The results revealed that the adsorbent is highly effective in removing OMPs. Common OMPs (i.e. carbamazepine, sulfamethoxazole and diclofenac) were completely removed from drinking water. Also, many of the PM substances were removed by more than 80% using an adsorbent dosage of 0.1 g/L. A strong relation between abatement of ultraviolet light absorbance at 254 nm (UV254) and OMP removal was observed. Therefore, UV254 abatement is a useful surrogate for a quick estimation of OMP removals.

β-Cyclodextrin/dialdehyde glucan-coated keratin nanoparticles for oral delivery of insulin

Successful oral insulin administration can considerably enhance the quality of life (QOL) of diabetes patients who must frequently take insulin injections. However, Oral insulin administration is seriously hampered by gastrointestinal enzymes, wide pH range, mucus and mucosal layers, which limit insulin oral bioavailability to ≤2 %. Herein, we developed a simple, inexpensive and safe dual β-cyclodextrin/dialdehyde glucan-coated keratin nanoparticle (β-CD-K-IN-DG). The resulted β-CD-K-IN-DG not only gave the ultra-high insulin loading (encapsulation efficiency (98.52 %)), but also protected insulin from acid and enzymatic degradation. This β-CD-K-IN-DG had a notable hypoglycemic effect, there was almost 80 % insulin release after 4 h of incubation under hyperglycemic conditions. Ex vivo results confirmed that β-CD-K-IN-DG possessed high mucus-penetration ability. Transepithelial transport and uptake mechanism studies revealed that bypass transport pathway and endocytosis promoted β-CD-K-IN-DG entered intestinal epithelial cells, thus increased the bioavailability of insulin (12.27 %). The improved stability of insulin during in vivo transport implied that β-CD-K-IN-DG might be a potential tool for the effective oral insulin administration.

Fabricating whole pine needles biomass with phenylhydrazine-4-sulphonic acid for effective removal of cationic dyes and heavy metal ions from wastewater

We applied a holistic, sustainable, and green approach to develop an effective multipurpose adsorbent from whole pine needles (PNs), a forest waste lignocellulosic biomass. The PNs were oxidized and modified with phenylhydrazine-4-sulphonic acid (ɸHSO3H) to OPN-ɸHSO3H. The latter was characterized and tested as an adsorbent for cationic dyes, malachite green (MG), methylene blue (MB), crystal violet (CV), and metal ions (Hg2⁺ and Pb2⁺). The adsorption followed different kinetic models: Elovich for MG and MB, pseudo-second-order for CV, and pseudo-first-order for Hg2⁺ and Pb2⁺. Langmuir isotherm indicated maximum adsorption capacities of 303.4 ± 8.91 mgg-1 (MG), 331.4 ± 17.50 mgg-1 (MB), 376.6 ± 22.47 mgg-1 (CV), 210.8 ± 28.86 mgg-1 (Hg2⁺), and 172.9 ± 20.93 mgg-1 (Pb2⁺) within 30 min. Maximum removal efficiencies were 99.0% (MG), 98.0% (MB), 96.04% (CV), 95.5% (Hg2⁺), and 89.8% (Pb2⁺). The adsorbent demonstrated significant regeneration and reusability over ten cycles, proving highly efficient for both cationic dyes and metal ions, with wide potential for practical applications where more than one adsorbate is present.

Assessment of potato surpluses as eco-friendly adsorbent for removal of Orange II: optimization and kinetic modelling at different pH values

Orange II, an azo dye used in textile and leather industries, is toxic and contributes to reducing dissolved oxygen in water. In this sense, agri-food waste adsorbents offer efficient, cost-effective dye removal. In this study, potato surpluses were evaluated as adsorbents for the removal of Orange II at 22 °C and pH values between 4 and 9. The adsorbents were characterized by their morphology, elemental composition, infrared spectra, and point of zero charge. Adsorption isotherms were analysed using Langmuir and Freundlich models, revealing that the Langmuir equation (0.933 < r2 > 0.882) better described the adsorption process compared to the Freundlich model (0.909 < r2 > 0.852). The maximum adsorption capacity at pH 4 was 1.1 and 2.3 times higher than at pH 7 and 9, respectively. This increased capacity at pH 4 was due to favourable electrostatic interactions between the cationic adsorbent surface and the anionic dye. A kinetic model was developed to understand the adsorption dynamics of Orange II, demonstrating high accuracy with coefficients of determination (r2) exceeding 0.99 across various pH values. The predictions of the kinetic model aligned well with the Langmuir isotherm results, indicating a strong theoretical foundation. The critical contact time required to achieve the minimum adsorbent concentration necessary for meeting a discharge limit of 14.7 mg L-1 was determined using both the Langmuir and kinetic models. Simulation profiles showed that when the adsorbent concentration was increased from 12 to 40 g L-1, the contact time necessary to achieve the discharge limit decreased from 26 to 3.35 h, highlighting the trade-off between contact time and cost. This study offers a cost-effective solution for wastewater treatment and presents a robust model for optimizing batch adsorption processes, marking a significant advancement in using potato surpluses for dye removal.

Evaluation of reduced graphene oxide from cotton waste as an efficient phenol adsorbent in aqueous media

The elimination of organic substances, such as phenol, in conventional and biological processes, has been considered a challenge for the petroleum industry. In this work, reduced graphene oxide (rGO), obtained from cellulosic biomass (CB-rGO), as cotton waste, was employed as a phenol adsorbent in an aqueous solution simulating refinery effluent. The CB-rGO was characterized using HRTEM, Raman, XRD, FTIR, BET, and zeta analysis. The behavior of variables such as pH, contact time, temperature, CB-rGO mass, and adsorbate concentration on the characteristics of the adsorption process were continuously investigated. These parameters of the adsorption process were evaluated across a range of adsorbent concentrations from 100 to 300 mg/L, pH in the range of 2-11, adsorbent mass 5-25 mg, contact time of 0-180 min, and temperature of 20-60 °C. The adsorption isotherm data were better described by the Freundlich equation compared to the Langmuir and Sips models, despite the small difference in R2 values. Mechanism diffusion was analyzed using the Boyd model and confirmed to be the rate-limiting step in the adsorption process. The endothermic nature of this CB-rGO adsorption process with phenol was confirmed by verifying the thermodynamic data. This successful removal of phenol from synthetic effluents highlights the promising potential of this adsorbent obtained from an industrial residue and being an ecologically more sustainable alternative compared to the synthesis of other materials identified to remove this contaminant.

Polyvinyl chloride nanoplastics transport inhibited in natural sandy soil by iron-modified biochar

The small particle size of nanoplastics allows them to migrate through soil and make them highly bioavailable, posing a potential threat to groundwater. Measures are urgently needed to reduce the migration of nanoplastics in soil. However, there is limited research available on this topic. In this study, two types of iron-modified biochar (magnetic corncob biochar (MCCBC) and magnetic walnut shell biochar (MWSBC)) were selected and their effects on the transport of polyvinyl chloride nanoplastics (PVC-NPs) in natural sandy soil columns under different ionic types and strengths were investigated. The results show that the transport of PVC-NPs in single sandy soil columns was rapid and efficient, with the estimated breakthrough rate of 85.10%. However, the presence of MCCBC and MWSBC (0.5%, w/w) significantly inhibited the transport of PVC-NPs in sandy soil columns (p < 0.05), and MCCBC had a stronger inhibitory effect on the transport of PVC-NPs than MWSBC. This can be attributed to the fact that the adsorption of PVC-NPs on adsorbents followed the order as: MCCBC > MWSBC > sandy soil. The retention of PVC-NPs by MCCBC and MWSBC is determined by ionic type and ionic strength. The presence of coexisting ions enhanced the inhibitory effect of iron-modified biochar on the transport of PVC-NPs, with the following order: Ca2+  > SO2- 4 > Cl- > NO- 3. The inhibitory effect of MCCBC and MWSBC on the transport of PVC-NPs in soil columns increased with increasing ionic strengths. Furthermore, MCCBC and MWSBC inhibited the migration of PVC-NPs in a rainwater-soil system. The mechanisms by which MCCBC and MWSBC affect the transport of PVC-NPs in soil columns were considered to enhancing adsorption and decreasing soil pore volume. The results provide new insights into the management of soil nanoplastic pollution.

Treating waste with waste: adsorption behavior and mechanism of phosphate in water by modified phosphogypsum biochar

The use of green methods to treat industrial waste and waste reuse has become a key environmental issue. In order to achieve this goal, this study treated waste phosphogypsum (PG) and produced modified PG biochar to adsorb and remove phosphorus from PG leachate, so that the PG pollution problem was controlled. In this study, PG was modified with sodium carbonate (Na2CO3) to prepare a modified PG biochar that was used for the removal of phosphorus-containing wastewater. An X-ray diffraction (XRD) analysis of the modified PG revealed that the main component was calcium carbonate (CaCO3), and a suitable amount of modified PG could load calcium oxide (CaO) onto the biochar and improve its physical properties. The experimental results showed that the modified PG biochar had a maximum phosphorus adsorption capacity of 132 mg/g. A further investigation of the mechanism of adsorption revealed the importance of electrostatic attraction and chemical precipitation, and it was found that the CaO in the modified PG biochar could effectively facilitate the conversion of phosphate to hydroxylapatite (Ca5(PO4)3OH) in water. The phosphorus removal rate from leachate obtained from a landfill containing PG was 99.38% for a specific dose of the modified PG biochar. In this study, a PG pollution control technology was developed to realize the goal of replacing waste with waste.

Utilizing olive leaves biomass as an efficient adsorbent for ciprofloxacin removal: characterization, isotherm, kinetic, and thermodynamic analysis

Olive leaves were utilized to produce activated biomass for the removal of ciprofloxacin (CIP) from water. The raw biomass (ROLB) was activated with sodium hydroxide, phosphoric acid, and Dead Sea water to create co-precipitated adsorbent (COLB) with improved adsorption performance. The characteristics of the ROLB and COLB were examined using SEM images, BET surface area analyzer, and ATR-FTIR spectroscopy. COLB has a BET surface area of 7.763 m2/g, markedly higher than ROLB's 2.8 m2/g, indicating a substantial increase in adsorption sites. Through investigations on operational parameters, the optimal adsorption efficiency was achieved by COLB is 77.9% within 60 min, obtained at pH 6, and CIP concentration of 2 mg/mL. Isotherm studies indicated that both Langmuir and Freundlich models fit the adsorption data well for CIP onto ROLB and COLB, with R2 values exceeding 0.95, suggesting effective monolayer and heterogeneous surface adsorption. The Langmuir model revealed maximum adsorption capacities of 636 mg/g for ROLB and 1243 mg/g for COLB, highlighting COLB's superior adsorption capability attributed to its enhanced surface characteristics post-modification. Kinetic data fitting the pseudo-second-order model with R2 of 0.99 for ROLB and 1 for COLB, along with a higher calculated qe for COLB, suggest its modified surface provides more effective binding sites for CIP, enhancing adsorption capacity. Thermodynamic analysis revealed that the adsorption process is spontaneous (∆Go < 0), and exothermic (∆Ho < 0), and exhibits a decrease in randomness (∆So < 0) as the process progresses. The ΔH° value of 10.6 kJ/mol for ROLB signifies physisorption, whereas 35.97 kJ/mol for COLB implies that CIP adsorption on COLB occurs through a mixed physicochemical process.

Phosphate recovery from aqueous phase using novel zirconium-based adsorbent

This study aims to document the phosphate ion (PO43-) adsorption capacity of a novel zirconium-based adsorbent. The physicochemical properties of the adsorbent are investigated using an array of methods and metrics such as electron microscopy, X-ray diffraction, thermal analysis, specific surface area, pore volume, pH point of zero charge (pHpzc), and surface hydroxyl groups. The batch method is used to elucidate PO43- adsorption capacity. Results suggested that the adsorption of PO43- was based on an internal diffusion and a monolayer adsorption. We also clarified that the pH of the solution significantly impacted the adsorption. Moreover, the adsorbent shows the ability to not only adsorb but also desorb PO43- for at least five cycles, based on an adsorption mechanism that we document. These findings indicate that this adsorbent could serve as a major industrial PO43- adsorbent.

Theoretical and Experimental Analysis of Hydroxyl and Epoxy Group Effects on Graphene Oxide Properties

In this study, we analyzed the impact of hydroxyl and epoxy groups on the properties of graphene oxide (GO) for the adsorption of methylene blue (MB) dye from water, addressing the urgent need for effective water purification methods due to industrial pollution. Employing a dual approach, we integrated experimental techniques with theoretical modeling via density functional theory (DFT) to examine the atomic structure of GO and its adsorption capabilities. The methodology encompasses a series of experiments to evaluate the performance of GO in MB dye adsorption under different conditions, including differences in pH, dye concentration, reaction temperature, and contact time, providing a comprehensive view of its effectiveness. Theoretical DFT calculations provide insights into how hydroxyl and epoxy modifications alter the electronic properties of GO, improving adsorption efficiency. The results demonstrate a significant improvement in the dye adsorption capacity of GO, attributed to the interaction between the functional groups and MB molecules. This study not only confirms the potential of GO as a superior adsorbent for water treatment, but also contributes to the optimization of GO-based materials for environmental remediation, highlighting the synergy between experimental observations and theoretical predictions in advances in materials science to improve sustainability.

Enhancing Methylene Blue Removal through Adsorption and Photocatalysis-A Study on the GO/ZnTiO3/TiO2 Composite

This study focuses on synthesizing and characterizing a graphene oxide/ZnTiO3/TiO2 (GO/ZTO/TO) composite to efficiently remove methylene blue (MB) from water, presenting a novel solution to address industrial dye pollution. GO and ZTO/TO were synthesized by the modified Hummers and sol-gel methods, respectively, while GO/ZTO/TO was prepared using a hydrothermal process. The structural and surface properties of the composite were characterized using various analytical techniques confirming the integration of the constituent materials and suitability for dye adsorption. The study revealed that GO/ZTO/TO exhibits an adsorption capacity of 78 mg g-1 for MB, with only a 15% reduction in adsorption efficiency until the fifth reuse cycle. Furthermore, the study suggests optimal adsorption near neutral pH and enhanced performance at elevated temperatures, indicating an endothermic reaction. The adsorption behavior fits the Langmuir isotherm, implying monolayer adsorption on homogeneous surfaces, and follows pseudo-second-order kinetics, highlighting chemical interactions at the surface as the rate-limiting step. The photocatalytic degradation of MB by GO/ZTO/TO follows pseudo-first-order kinetics, with a higher rate constant than that of GO alone, demonstrating the enhanced photocatalytic activity of the composite. In conclusion, GO/ZTO/TO emerges as a promising and sustainable approach for water purification, through an adsorption process and subsequent photocatalytic degradation.

Reuse of polymeric waste for the treatment of marine water polluted by diesel

Accidental diesel spills can occur in marine environments such as harbors, leading to adverse effects on the environmental compartment and humans. This study proposes the surgical mask as an affordable and sustainable adsorbent for the remediation of diesel-contaminated seawater to cope with the polymeric waste generated monthly in hospital facilities. This approach can also be helpful considering a possible future pandemic, alleviating the pressure on the waste management system by avoiding improper mask incineration and landfilling, as instead occurred during the previous COVID-19. Batch adsorption-desorption experiments revealed a complete diesel removal from seawater after 120 min with the intact laceless mask, which showed an adsorption capacity of up to 3.43 g/g. The adsorption curve was better predicted via Weber and Morris's kinetic (R2 = 0.876) and, in general, with Temkin isotherm (R2 = 0.965-0.996) probably due to the occurrence of chemisorption with intraparticle diffusion as one of the rates-determining steps. A hysteresis index of 0.23-0.36 was obtained from the desorption isotherms, suggesting that diesel adsorption onto surgical masks was faster than the desorption mechanism. Also, the effect of pH, ionic strength and temperature on diesel adsorption was examined. The results from the reusability tests indicated that the surgical mask can be regenerated for 5 consecutive cycles while decreasing the adsorption capacity by only approximately 11%.

Evaluation of Phenobarbital Adsorption Efficiency on Biosorbents or Activated Carbon Obtained from Adansonia Digitata Shells

The removal of pharmaceutically active compounds present in relatively low concentration in wastewater is critical. This is because they have a severe, negative impact on life and the environment. To address this issue, adsorption was used, which is an effective wastewater treatment method for removing substances found in low concentrations in water. This study compared the adsorption performance of active carbon to three biosorbents derived from Adansonia digitata shells. The adsorbents were prepared and characterized using TGA, SEM, EDX, and FTIR analyses and pHPZC. To better understand the adsorption process, equilibrium and reaction kinetics studies were conducted. The effect of contact time, initial phenobarbital concentration, adsorbent mass, and pH was investigated in static conditions. The adsorption results revealed that the biosorbent B3 has a higher affinity for the eliminated compound, with an equilibrium time of 60 min and an adsorption capacity of 47.08 mg/g at an initial concentration of 50 mg/L. The experimental data are consistent with Langmuir and Sips adsorption isotherm models, and with the pseudo-second order and Elovich models for kinetics description. This indicates strong interactions between the adsorbent materials and the pharmaceutical micropollutant. Based on these findings, it appears that, among the tested materials, B3 biosorbent is the most efficient for removing phenobarbital present in low concentrations in water.

A two-in-one thiosemicarbazide and whole pine needle-based adsorbent for rapid and efficient adsorption of methylene blue dye and mercuric ions

Herein, we report the synthesis of an oxidized pine needle-thiosemicarbazone Schiff base (OPN-TSC) from whole pine needles (WPN) as a dual-purpose adsorbent to remove a cationic dye, methylene blue (MB), and Hg2+ ions in separate processes. The adsorbent was synthesized by periodate oxidation of WPN followed by a reaction with thiosemicarbazide. The syntheses of OPN and OPN-TSC were confirmed by FTIR, XRD, FESEM, EDS, BET, and surface charge analysis. The emergence of new peaks at 1729 cm-1 (-CHO stretching) and 1639 cm-1 (-COO- stretching) in the FTIR spectrum of OPN confirmed the oxidation of WPN to OPN. FTIR spectrum of OPN-TSC has a peak at 1604 cm-1 (C = N stretching), confirming the functionalization of OPN to OPN-TSC. XRD studies revealed an increase in the crystallinity of OPN and a decrease in the crystallinity of OPN-TSC because of the attachment of thiosemicarbazide to OPN. The values of %removal for MB and Hg2+ ions by OPN-TSC were found to be 87.36% and 98.2% with maximum adsorption capacity of 279.3 mg/g and 196 mg/g for MB and Hg2+ ions, respectively. The adsorption of MB followed pseudo-second-order kinetics with correlation coefficient (R2 of 0.99383) and Freundlich isotherm (R2 = 0.97239), whereas Hg2+ ion removal demonstrated the Elovich (R2 = 0.97076) and Langmuir isotherm (R2 = 0.95110). OPN-TSC is regenerable with significant recyclability up to 10 cycles for both the adsorbates. The studies established OPN-TSC as a low-cost, sustainable, biodegradable, environmentally benign, and promising adsorbent for the removal of hazardous cationic dyes and toxic metal ions from wastewater and industrial effluents, especially the textile effluents.

Adsorption of hexavalent chromium from wastewater using polyaniline-coated microcrystalline cellulose nanocomposites

In this study, the effectiveness of microcrystalline cellulose (MCC) as an adsorbent for the removal of hexavalent chromium, Cr(vi), from synthetic wastewater was enhanced through functionalization with polyaniline (PANI). Scanning electron microscopy (SEM) showed that MCC was an effective scaffold for in situ chemical oxidative polymerization of aniline. Fourier transform infrared spectroscopy (FTIR) spectroscopy and X-ray diffraction confirmed successful PANI synthesis. The MCC/PANI nanocomposites exhibited relatively high specific surface areas, compared to that of the MCC (2.05 m2 g-1). Batch adsorption studies showed that the optimal conditions for the removal of Cr(vi) from wastewater using the MCC/PANI-69 wt% nanocomposite were an initial Cr(vi) concentration of 100 mg L-1, an adsorbent dosage of 4 g L-1 and a Cr(vi) solution pH of 7. The MCC/PANI-69 wt% required only 30 min to reach equilibrium and the equilibrium removal efficiency was 95%. FTIR spectroscopy and energy dispersive X-ray spectrometry results suggest that the Cr(vi) removal mechanism by the MCC/PANI-69 wt% nanocomposite at pH 7 was through electrostatic attraction of Cr(vi) species by PANI, reduction of Cr(vi) into Cr(iii) and precipitation of Cr(iii) on the nanocomposite surface. The kinetics for the removal of the Cr(vi) by the MCC/PANI-69 wt% nanocomposite were adequately described by the pseudo second order (PSO) kinetics model, whereas the Langmuir isotherm adequately described the equilibrium data. The MCC/PANI-69 wt% nanocomposite had a significantly improved maximum adsorption capacity of 35.97 mg g-1, at pH 7, in comparison to that of the MCC (3.92 mg g-1 at pH 1). The study demonstrated that, whereas most of the reported adsorbents for Cr(vi) are only effective at low pH values, the MCC/PANI nanocomposite synthesized in this study was effective at pH 7.

Adsorption of Cd(II) ions on magnetic graphene oxide/cellulose modified with β-cyclodextrin: Analytical interpretation via statistical physics modeling and fractal like kinetic approach

In the present study, β-cyclodextrin modified magnetic graphene oxide/cellulose (CN/IGO/Cel) was fabricated for removal of Cd(II) ions. The material was characterized through various analytical techniques like FTIR, XRD, TGA/DTA, SEM, TEM, and XPS. The point of zero charge of the material was obtained as 5.38. The controllable factors were optimized by Taguchi design and optimum values were: adsorbent dose-16 mg, equilibrium time-40 min, and initial concentration of Cd(II) ions-40 mg/L. The material shows high adsorption capacity (303.98 mg/g). The good fitting of Langmuir model to adsorption data (R2 = 0.9918-0.9936) revealed the monolayer coverage on adsorbent surface. Statistical physics model M 2 showed best fitting to adsorption data (R2 > 0.997), suggesting the binding of Cd(II) ions occurred on two different receptor sites (n). Stereographically n > 1 confirming vertical multi-molecular mechanisms of Cd(II) ions adsorption on CN/IGO/Cel surface. The adsorption energies (E1 = 23.71-28.95 kJ/mol; E2 = 22.69-29.38 kJ/mol) concluded the involvement of physical forces for Cd(II) ions adsorption. Kinetic data fitted well to fractal-like pseudo first-order model (R2 > 0.9952), concluding the adsorption of Cd(II) ions occurred on energetically heterogeneous surface. The kinetic analysis shows that both the film-diffusion and pore-diffusion were responsible for Cd(II) ions uptake. XPS analysis was utilized to explain the adsorption mechanism of Cd(II) ions onto CN/IGO/Cel.

The use of banana peel as a low-cost adsorption material for removing hexavalent chromium from tannery wastewater: optimization, kinetic and isotherm study, and regeneration aspects

When the concentration of hexavalent chromium (Cr(vi)) in the environment is greater than a certain limit, it becomes a global concern. Thus, the aim of this study was to use banana peel as an adsorbent to remove heavy metals, specifically Cr(vi) ions from wastewater. Banana peel (BP) was activated in a furnace for 2 h (h) at 450 °C and 50% humidity. Subsequently, the activated BP was characterized by proximate analysis, elemental analysis, scanning-electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer Emmett Teller (BET) analysis, and thermogravimetric analysis (TGA). According to the characterization results, the activated BP possessed a porous surface and high surface area of 200 m2 g-1, which are important adsorption parameters. Additionally, the removal efficiency for Cr(vi) was evaluated in terms of pH, contact time, initial concentration, and adsorbent dose. Consequently, the optimal operating conditions for removing 94% of Cr(vi) were found to be an adsorption time of 92 min, adsorbent dose of 1.5 g L-1, pH of 3, and initial Cr(vi) concentration of 38 mg L-1. In addition, the adsorption kinetics and isotherms were examined. The pseudo-first-order model with an R2 of 0.996 and the Langmuir isotherm with an R2 of 0.997 were found to be the most effective mathematical representations of the rate and nature of Cr(vi) adsorption on the surface of the activated BP, respectively. Furthermore, it was discovered that the activated BP could be reused six times before its removal efficiency was reduced to less than 70%.

Imidazolate framework material for crude oil removal in aqueus media: Mechanism insight

Considerable amount of produced water discharged by the oil industry contributes to an environmental imbalance due to the presence of several components potentially harmful to the ecosystem. We investigated the factors influencing the adsorption capacity of Zinc Imidazolate Framework-8 (ZIF-8) in finite bath systems for crude oil removal from petroleum extraction in synthetic produced water. ZIF-8, experimentally obtained by solvothermal method, was characterized by XRD, FTIR, TGA, BET and its point of zero charge (pHpcz) was determined. Synthesized material showed high crystallinity, with surface area equal to 1558 m2 g-1 and thermal stability equivalent to 400 °C. Adsorption tests revealed, based on the Sips model, that the process takes place in a heterogeneous system. Additionally, intraparticle diffusion model exhibited multilinearity characteristics during adsorption process. Thermodynamic investigation demonstrated that adsorption process is spontaneous and exothermic, indicating a physisorption phenomenon. These properties enable the use of ZIF-8 in oil adsorption, which presented an adsorption capacity equal to 452.9 mg g-1. Adsorption mechanism was based on hydrophobic interactions, through apolar groups present on ZIF-8 structure and oil hydrocarbons, and electrostatic interactions, through the difference in charges between positive surface of adsorbent and negatively charged oil droplets.

Identification and assessment of appropriate remediation management techniques for the recovery of soil-like material produced in landfill mining

Landfill mining has received major attention in recent years for the reclamation of waste disposal sites, including in developing countries such as India where significant efforts are being made to manage sites in this way. The bulk of the material obtained from landfill mining consists of fine-grained soil-like material (SLM) but its direct reuse in off-site applications is restricted due to the presence of harmful heavy metals, soluble salts and other pollutants. In this study, appropriate techniques for managing SLM to permit recovery and reuse are assessed. As a result, experimental investigation explores the efficacy of two remediation techniques considered appropriate for SLM management: electrokinetic remediation and phytoremediation. These were applied to SLM from a recently mined landfill and their ability to reduce heavy metal and other soluble salt burdens assessed. Electrokinetic remediation has shown considerable potential to mobilise and transport heavy metals and soluble salts through and from the SLM over an eight-week period. Phytoremediation experiments also demonstrated mobilisation and uptake of metals from the SLM over a similar duration although relatively low amounts were recovered as a result of the low biomass produced over this period. Both technologies have demonstrated potential for recovery of metals from SLM, as well as recovering the SLM itself as a potential resource.

Evaluation of the lead and chromium removal capabilities of Bacillus subtilis-induced food waste compost-based biomedia

Food waste compost (FWC) is a sustainable recycling approach employed in soil media, offering extensive advantages to urban areas by promoting resource circulation and effectively managing water pollution. To improve value, Bacillus subtilis (B. subtilis)-induced FWC-based biomedia (BIBMFWCs) was produced via a secondary treatment involving selective meso-thermophilic stages. During the production of BIBMFWCs, physicochemical properties were found to have favorable characteristics for the efficient removal of metal ions. The produced organic-carbonate complex structure demonstrated the synergistic effect involving simultaneous sorption/precipitation mechanisms for the removal of Pb(II) and Cr(III). Also, the dose of B. subtilis has an impact on the pseudo-second-order (PSO) and intra-particle diffusion (IPD) reaction, leading to distinct removal capacities for Pb(II) and Cr(III) [24.26-24.74 mg g-1 in Pb(II) and 12.7-23.93 mg g-1 in Cr(III)]. Furthermore, B. subtilis, an inducing mediator for microbial metabolites, exhibits the potential to facilitate the removal of Pb(II) and Cr(III) through biological modification of raw materials, which are transformed, facilitating the presence of hydroxyl groups, immobilizing metal ions, and enabling ion exchange via biogenic carbonate formation processes. Finally, the developed BIBMFWCs could be used as a nature-based solution (NBS) material without in-situ pH control.

Functional Ag-EDTA-modified MnO2 nanocoral reef for rapid removal of hazardous copper from wastewater

A novel MnO2@EDTA-Ag nanocoral reef was constructed via a simplified redox reaction followed by EDTA and Ag nanoparticles impregnation to capture hazardous copper (II) from wastewater. A comprehensive characterization of the synthesized materials was conducted. The morphology of MnO2@EDTA-Ag in the form of a nanocoral reef was constructed of two-dimensional nanoplatelets and nanorod-like nanostructures. The optimal adsorption conditions proposed by the Plackett-Burman design (PBD) that would provide a removal % of 99.95 were pH 5.5, a contact time of 32.0 min, a Cu(II) concentration of 11.2 mg L-1, an adsorbent dose of 0.05 g, and a temperature of 40.3 °C. The loading of Ag nanoparticles onto MnO2@EDTA improved the adsorption capability of MnO2@EDTA-Ag. Additionally, the recyclability of MnO2@EDTA-Ag nanocoral reef was maintained at 80% after three adsorption-desorption cycles, and there was no significant change in the XRD analysis before and after the recycling process, implying its stability. It was found that nanocoral reef-assisted EDTA formed a chelation/complexation reaction between COO- groups and C-N bonds of EDTA with Cu(II) ions. In addition, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis proved the synergistic effect of the electrostatic interaction and chelation/complexation was responsible for the removal mechanism of Cu(II). Also, the results demonstrated no significant variation in MnO2@EDTA-Ag removal efficiency for all the tested real water samples, revealing its efficacy in wastewater treatment. Therefore, the current study suggests that MnO2@EDTA-Ag has substantial potential to be used as a feasible adsorbent for probable hazardous metals remediation.

Cyanide Removal by ZnTiO3/TiO2/H2O2/UVB System: A Theoretical-Experimental Approach

Cyanide is a highly toxic substance present in wastewater from various industries. This study investigates the removal of cyanide species (CS) from aqueous solutions using the ZnTiO3/TiO2/H2O2/UVB system. ZnTiO3/TiO2 nanoparticles synthesized by the sol-gel method were characterized by powder X-ray diffractometry (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The adsorption capacity of nanoparticles was tested by varying the pH of the solution, adsorbent concentration, and contact time. The adsorption of CS on ZnTiO3 and TiO2 surfaces was verified by Density Functional Theory (DFT) calculations. Photocatalytic experiments were achieved under UVB irradiation (λ = 310 nm). The response surface methodology (RSM) was used to optimize the CS removal efficiency. The detoxification effect was evaluated by acute toxicity tests with brine shrimp. The theoretical results show that the adsorption of CS is energetically more favorable on the ZnTiO3 surface than on the TiO2 surface. The experimental results show that the system consisting of ZnTiO3/TiO2 (200 mg L-1), H2O2 (0.1%), and UVB light removes 99% of CS from aqueous solutions after 60 min and reduces the mortality of nauplii in 90% after 90 min. This system was reused in five consecutive cycles with a total loss of efficiency of 30%.

Magnetite nanoparticles decorated on cellulose aerogel for p-nitrophenol Fenton degradation: Effects of the active phase loading, cross-linker agent and preparation method

Magnetite nanoparticles (Fe3O4 NPs) are among the most effective Fenton-Like heterogeneous catalysts for degrading environmental contaminants. However, Fe3O4 NPs aggregate easily and have poor dispersion stability because of their magnetic properties, which seriously decrease their catalytic efficiency. In this study, a novel environmentally friendly method for synthesising Fe3O4@CA was proposed. Fe3O4 NPs were immobilized on the 3D cellulose aerogels (CAs) in order to augment the degradation efficiency of p-nitrophenol (PNP) treatment and make the separation of the catalyst accessible by vacuum filtration method. Besides, CAs were fabricated from a cellulose source extracted from water hyacinth by using different cross-linking agents, such as kymene (KM) and polyvinyl alcohol-glutaraldehyde system (PVA-GA), and other drying methods, including vacuum thermal drying and freeze drying, were evaluated in the synthesis process. As-synthesized samples were analysed by various methods, including Powder X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis and Brunauer-Emmett-Teller. Then, using ultraviolet-visible spectroscopy, the difference in the degradability of PNP of the obtained material samples was also investigated to determine their potential applications. Results highlighted that the Fe3O4-3@CA-KF catalyst with an Fe3O4 loading of 0.40 g/gCA used KM as a cross-linker and the freeze-drying method demonstrated the highest PNP removal efficiency (92.5 %) in all Fe3O4@CA samples with a H2O2 content of 5 g/L. The degradation kinetics and well-fitted pseudo-first-order model were investigated. Notably, after five successive PNP degradation experiments, this catalyst retained ∼80 % of the ability to degrade PNP, indicating its outstanding reusability. In environmental remediation, this study provides valuable insights into the development of simply separated and high-efficiency catalysts for heterogeneous catalytic reactions.

Predicting the removal efficiency of pharmaceutical and personal care products using heated metal oxides as adsorbents based on their physicochemical characteristics

Pharmaceutical and personal care products (PPCPs) are emerging pollutants that are commonly found in the environment and exist predominantly in nondegradable forms. Several attempts have been made to remove PPCPs via conventional wastewater treatment processes; however, these processes have limitations, such as high costs and insufficient removal efficiencies. Adsorption is a promising alternative for removing PPCPs because it is inexpensive, highly reusable, and easy to operate. Therefore, this study aims to determine the contributing characteristics that can be used to predict the adsorption behaviour of PPCPs based on their physicochemical properties, with heated metal oxide adsorbents (HMOAs). HAOP (heated aluminium oxide particles) and HIOP (heated iron oxide particles) with particle sizes below 38 μm were used. Results from the Brunauer-Emmett-Teller (BET) analysis show that HIOP has higher surface area and smaller pore size (113.7 ± 26.3 m2/g and 5.4 ± 1.8 nm) than HAOP (14.5 ± 0.6 m2/g and 18.6 ± 3.1 nm), which suggest that HIOP would show superior adsorption rates compared to HAOP. The adsorption mechanism is identified based on three major physicochemical properties of PPCPs: molecular weight (M.W.), octanol-water partition coefficient (log Kow), and acid dissociation constant (pKa). The results suggest that the most dominant factor that contributes to the adsorption of PPCPs on to HMOAs is the M.W., where the larger the molecular size, the better the adsorption efficiency. The tests conducted with varying log Kow values revealed that the hydrophilicity of the adsorbent influences the adsorption performance. It was found that HIOP exhibits better removal efficiencies with hydrophilic PPCPs (up to 83%) than with hydrophobic PPCPs (48%), while HAOP exhibits better removal efficiencies with hydrophobic PPCPs (86%) than with hydrophilic PPCPs, with less than 10% removal. Unlike the M.W. and pKa values, the log Kow does not exhibit any visible trend. Therefore, the adsorption behaviour can be predicted with the M.W. and pKa values of the PPCPs, when HAOP and HIOP are used as adsorbents.

Raw sawdust utilization for the removal of acid red57 and basic fuchsin dyes from aqueous solution: equilibrium, kinetics, and thermodynamic investigation

The aim of work is the use of a cheap adsorbent; sawdust (SD), for the adsorption of anionic dye, acid red57 (AR57), and cationic dye, basic fuchsin (BF). The adsorption of AR57 and BF on SD increased by increasing contact time and adsorbent dosage, while decreased with the increase of temperature and initial dye concentration. The increase in pH decreased the adsorption of AR57 and increased the adsorption of BF. The effective pH, adsorbent dose, and contact time on the AR57 removal efficiency were found to be 3, 0.1 g and 50 min, respectively. While for BF it was found to be 6, 0.2 g and 50 min, respectively. Fitting equilibrium data to Langmuir, Freundlich and Temkin isotherms showed that Freundlich model is the most suitable to describe the acid red57 and basic fuchsin. The kinetic studies indicate that the adsorption of AR57 and BF follows a pseudo-second-order model. The adsorption of both AR57 and BF is spontaneous (ΔG = -3.97, -3.27 kJ/mol) and exothermic (ΔH = -22.9, -8.3 kJ/mol) with negative values of ΔG and ΔH. The negative values of ΔS of both AR57 and BF (ΔS = -64.6, -16.7 J/mol. K) showed that the randomness decreases through the adsorption process.

Adsorption of Methyl Red and Methylene Blue on Carbon Bioadsorbents Obtained from Biogas Plant Waste Materials

In this study, biocarbon was obtained from the waste material corn digest. Carbon adsorbents were obtained by physical activation of the precursor with CO2. Detailed physicochemical characterization of the biocarbon was carried out using low-temperature nitrogen adsorption/desorption, Boehm titration, zero-charge point (pHpzc) and iodine number. In addition, the sorption capacity of the biocarbon agents towards an aqueous solution of methylene blue and methyl red was determined, and the kinetics of the adsorption process were determined. The biocarbon adsorbents were characterized by an average developed specific surface area covering the range from 320 to 616 m2/g. The sorption capacity of the biocarbon adsorbents against methylene blue ranged from 40 mg/g to 146 mg/g, and for methyl red it covered the range from 31 mg/g to 113 mg/g. It was shown that the efficiency of organic dye removal by the obtained biocarbons depends on the initial concentration of the adsorbate solution, its mass, shaking rate, adsorbent-adsorbate contact time and temperature. The results obtained from the Langmuir and Freundlich kinetic models showed that the Langmuir model is the most suitable model for describing the adsorption of the studied pollutants on biocarbon. In turn, the adsorption kinetics of dyes is described according to the pseudo-second-order model. Adsorption studies also showed that as the process temperature increases, the removal efficiency of methylene blue and methyl red increases.

Porous Geopolymer/ZnTiO3/TiO2 Composite for Adsorption and Photocatalytic Degradation of Methylene Blue Dye

In this study, GP (geopolymer) and GTA (geopolymer/ZnTiO₃/TiO₂) geopolymeric materials were prepared from metakaolin (MK) and characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive X-rays (EDX), specific surface area (SSA), and point of zero charge (PZC). The adsorption capacity and photocatalytic activity of the compounds prepared in the form of pellets was determined by degradation of the methylene blue (MB) dye in batch reactors, at pH = 7.0 ± 0.2 and room temperature (20 °C). The results indicate that both compounds are highly efficient at adsorbing MB, with an average efficiency value of 98.5%. The Langmuir isotherm model and the pseudo second order kinetic model provided the best fits to the experimental data for both compounds. In the MB photodegradation experiments under UVB irradiation, GTA reached an efficiency of 93%, being higher than that achieved by GP (4%). Therefore, the incorporation of ZnTiO₃/TiO₂ in the geopolymeric matrix allowed GTA to achieve higher overall efficiency, by combining adsorption and photocatalysis, compared to the GP compound. The results indicate that the synthesized compounds could be used for up to five consecutive cycles for the removal of MB from wastewater through adsorption and/or photocatalysis processes.

Removal of pristine and aged microplastics from water by magnetic biochar: Adsorption and magnetization

Adsorption is an efficient and eco-friendly removal technique for small pristine microplastics in water. However, small pristine microplastics are not representative of those large microplastics in natural water with different aging levels. Whether the adsorption technique is effective in removing large aged microplastics from water remained unknown. To this end, the removal efficiency of large polyamide (PA) microplastics with different aging time by magnetic corncob biochar (MCCBC) was evaluated under different experimental conditions. After treated by heated-activated potassium persulfate, the physicochemical properties of PA have changed dramatically, as evidenced by rough surface, decreased particle size and crystallinity, and increased oxygen-containing functional groups, which enhanced with aging time. These changes promoted the combination of aged PA and MCCBC, thereby resulting in a higher removal efficiency of aged PA (~97 %) than that of pristine ones (~25 %). It is supposed that the adsorption process was a result of complexation, hydrophobic interaction, and electrostatic interaction. Increased ionic strength inhibited the removal of both pristine and aged PA, and neutral pH conditions favored PA removal. Furthermore, particle size played a great role in the removal of aged PA microplastics. When the particle size of aged PA was smaller than 75 μm, their removal efficiency was significantly increased (p < 0.01). The small PA microplastics were removed by adsorption, whereas the large ones were removed by magnetization. These research findings highlight magnetic biochar as promising technique for removing environmental microplastics.

Faujasite-Type Zeolite Obtained from Ecuadorian Clay as a Support of ZnTiO3/TiO2 NPs for Cyanide Removal in Aqueous Solutions

In this study, zeolites prepared by the hydrothermal method from Ecuadorian clay were combined with the precursor clay and with the semiconductor ZnTiO₃/TiO₂ prepared by the sol-gel method to adsorb and photodegrade cyanide species from aqueous solutions. These compounds were characterized by X-ray powder diffraction, X-ray fluorescence, scanning electron microscopy, energy-dispersive X-rays, point of zero charge, and specific surface area. The adsorption characteristics of the compounds were measured using batch adsorption experiments as a function of pH, initial concentration, temperature, and contact time. The Langmuir isotherm model and the pseudo-second-order model fit the adsorption process better. The equilibrium state in the reaction systems at pH = 7 was reached around 130 and 60 min in the adsorption and photodegradation experiments, respectively. The maximum cyanide adsorption value (73.37 mg g^-1) was obtained with the ZC compound (zeolite + clay), and the maximum cyanide photodegradation capacity (90.7%) under UV light was obtained with the TC compound (ZnTiO₃/TiO₂ + clay). Finally, the reuse of the compounds in five consecutive treatment cycles was determined. The results reflect that the compounds synthesized and adapted to the extruded form could potentially be used for the removal of cyanide from wastewater.

Preparation and characterization of chemically cross-linked zwitterionic copolymer hydrogel for direct dye and toxic trace metal removal from aqueous medium

In this work, a zwitterionic copolymer hydrogel with adsorption affinity toward anionic dye and cationic trace metal was prepared by a free radical copolymerization of cationic ([3-(methacryloylamino)propyl] trimethylammonium chloride (MPTC)) and anionic (sodium 4-vinylbenzenesulfonate (SVBS)) monomers. Bis[2-(methacryloyloxy)ethyl] phosphate was used as a cross-linker and its effect on the adsorption properties of the prepared hydrogel was evaluated. The prepared materials were characterized by FTIR, XRD, SEM, EDX, and N₂ adsorption at 77 K analysis. FTIR and EDX analysis demonstrated the successful preparation of poly(MPTC-co-VBS). XRD and SEM analysis showed that the poly (MPTC-co-VBS) is amorphous and has quasi-honeycomb morphology with large pores. Increasing the amount of the cross-linker enhanced the adsorption of direct blue 71 dye (DB71) and Pb(II) ions. The highest removal of DB71 and Pb(II) was achieved after 2 h using 1.5 g/L of poly(MPTC-co-VBS); however, the optimum solution pH was 3 for DB71 and 5 for Pb(II). The kinetics and isotherm studies illustrated that the surface of poly(MPTC-co-VBS) is heterogenous with small-sized homogenous pitches and the DB71 and Pb(II) adsorption onto poly(MPTC-co-VBS) is favorable. Finally, poly(MPTC-co-VBS) is more efficient in removing DB71 and Pb(II) from aqueous solutions than many other reported adsorbents.

Titania/reduced graphene oxide nanocomposites (TiO2/rGO) as an efficient photocatalyst for the effective degradation of brilliant green in aqueous media: effect of peroxymonosulfate and operational parameters

This study is focused on synthesis of highly efficient Titania/reduced Graphene Oxide (TiO₂/rGO) nanocomposites by means of simple hydrothermal technique. The TiO₂/rGO were synthesized in different ratios of 0.5, 1.0, 2.0, and 3% by varying the concentration of rGO while the concentration of TiO₂ was kept constant and the obtained samples were designated as TrG0.5, TrG1, TrG2, and TrG3 respectively. Different characterization techniques (SEM, TEM, HRTEM, XRD, EDX, TGA, UV-DRS, PL, EIS, and BET) showed high crystallinity, small crystallite size (18.4 nm), high thermal stability, high purity, low band gap energy (E_g = 3.12 eV), and high surface area (65.989 m²/g) for the as-synthesized TiO₂/rGO nanocomposite. The efficiencies of TiO₂/rGO were determined in terms of brilliant green (BG) dye degradation in aqueous media under UV light. The results revealed that 2% TiO₂/rGO (TrG2) showed high efficiency for BG degradation with the k_app of 0.023 min^-1 compared to TiO₂ alone (k_app of 0.006 min^-1). The rate of BG degradation was further synergised by the addition of peroxymonosulfate (PMS) to the system. The degradation of BG was improved to 99.4% by the incorporation of PMS in aqueous media compared to TrG2 alone. Furthermore, the degradation of BG was also examined in various media (neutral, acidic, and basic). The results revealed that by increasing pH of the medium from 3.85 to 8.2 the degradation of BG was enhanced from 99.4 to 99.9% with the corresponding k_app of 0.0602 min^-1. Moreover, the photocatalytic degradation of BG followed the pseudo-first-order kinetics. Radical scavenging experiments showed that ^●OH and SO₄^●- were the main species responsible for the degradation of BG under UV light. Besides, for determining the efficiency of as-synthesized TrG2/PMS system, the degradation of BG was also performed in various water types (distilled water, tape water, synthetic wastewater, and industrial wastewater). The degradation products (DPs) of BG and their corresponding pathways were proposed, accordingly.

Restricted access polypyrrole employed in pipette-tip solid-phase extraction for determination of nimodipine and nicardipine in breast milk

A HPLC-UV method for the determination of nimodipine and nicardipine in breast milk using restricted access polypyrrole as an adsorbent in pipette-tip solid-phase extraction (PT-SPE) has been developed. The chromatographic conditions were a C₁₈ column (150 mm × 4.60 mm, 5 μm) using methanol : acetonitrile : ultrapure water (55 : 30 : 15, v/v/v) at a flow rate of 1.0 mL min^-1 and detection at 236 nm. The adsorbents have been synthesized and characterized by using Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, surface analysis, wettability and point zero charge, and were then applied in sample preparation. The main parameters that affect analyte recovery from breast milk by PT-SPE were optimized and the analytical method showed recoveries around 100%, linearity from 3 to 3000 ng mL^-1, and correlation coefficients (r) ≥ 0.99 for the two analytes, in addition to adequate precision, accuracy and robustness. Finally, the validated method has been successfully applied in analyses of breast milk from volunteers.

From polyethylene waste bottles to UIO-66 (Zr) for preconcentration of steroid hormones from river water

Metal-organic framework (UiO-66 (Zr) was synthesized using polyethylene terephthalate (PET) and used as an adsorbent for extraction and preconcentration of steroid hormones in river water. Polyethylene waste bottles were used as the source of polyethylene terephthalate (PET) ligands. The UIO-66(Zr), which the PET was made from recycled waste plastics, was used for the first time for the extraction and preconcentration of four different types of steroid hormones in river water samples. Various analytical characterization techniques were employed to characterize the synthesized material. The steroid hormones were detected and quantified using high-performance liquid chromatography coupled with diode array detector (HPLC-DAD). The results were further validated using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Experimental variables, such as sample pH, the mass of adsorbent and extraction time, were optimized using Box-Behnken design (BBD). The dispersive solid phase extraction method combined with HPLC-DAD, displayed good linearity (0.004-1000 µg/L) low limits of detections (LODs, 1.1-16 ng/L for ultrapure water and 2.6-5.3 ng/L for river water) and limits of quantification (LOQs, 3.7-5.3 ng/L for ultrapure water and 8.7-11.0 ng/L for river water samples) and acceptable extraction recoveries (86-101%). The intraday (n = 10) and interday (n = 5) precisions expressed in terms of relative standard deviations (%RSD) were all less than 5%. The steroid hormones were detected in most of the river water samples (Vaal River and Rietspruit River). The DSPE/HPLC method offered a promising approach for simultaneous extraction, preconcentration and determination of steroid hormones in water.

Synthesis of nanomagnetite/copper oxide/potassium carrageenan nanocomposite for the adsorption and Photo-Fenton degradation of Safranin-O: kinetic and thermodynamic studies

In the current study, a novel nanomaterial called nanomagnetite/copper oxide/potassium carrageenan nanocomposite (MKCO) was fabricated to include Fenton (nanomagnetite, NM) and Fenton-like reagent (copper oxide nanoparticles, NCO) in a matrix of potassium carrageenan biopolymer. The prepared solid materials were characterized by different physicochemical techniques, such as TGA, N2 adsorption/desorption, SEM, TEM, XRD, DRS, pHPZC, and FTIR. The prepared MKCO showed unique properties like higher specific surface area of 652.50 m2/g, pore radius of 1.19 nm, pHPZC equals 7.80, and the presence of different surface chemical functional groups. Under various application conditions, comparative experiments between Safranin-O dye (SO) adsorption and Photo-Fenton catalytic degradation were conducted. After 24 h, MKCO had a maximum adsorption capacity of 384.61 mg/g at 42 °C, while the Photo-Fenton oxidation process took only 10 min to totally decompose 93% of SO at 21 °C. Based on the higher values of correlation coefficients, Langmuir’s adsorption model is the best-fitted adsorption model for SO onto all the prepared solid materials. Studies on SO adsorption’s kinetics and thermodynamics show that it is physisorption and that it operates according to endothermic, spontaneous, and PFO model processes. While, PFO, endothermic, and non-spontaneous processes are satisfied by the catalytic decomposition of SO. After five application cycles, MKCO demonstrated good catalyst reusability with a 3.4% decrease in degrading efficiency. For lower contaminant concentrations and shorter application times, Photo-Fenton catalytic degradation of organic pollutants is more effective than adsorption.

Graphical abstract

Fenton and Photo-Fenton degradation of Safranin-O

Effect of Doping TiO2 NPs with Lanthanides (La, Ce and Eu) on the Adsorption and Photodegradation of Cyanide-A Comparative Study

Free cyanide is a highly dangerous compound for health and the environment, so treatment of cyanide-contaminated water is extremely important. In the present study, TiO₂, La/TiO₂, Ce/TiO₂, and Eu/TiO₂ nanoparticles were synthesized to assess their ability to remove free cyanide from aqueous solutions. Nanoparticles synthesized through the sol-gel method were characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transformed infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and specific surface area (SSA). Langmuir and Freundlich isotherm models were utilized to fit the adsorption equilibrium experimental data, and pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to fit the adsorption kinetics experimental data. Cyanide photodegradation and the effect of reactive oxygen species (ROS) on the photocatalytic process were investigated under simulated solar light. Finally, reuse of the nanoparticles in five consecutive treatment cycles was determined. The results showed that La/TiO₂ has the highest percentage of cyanide removal (98%), followed by Ce/TiO₂ (92%), Eu/TiO₂ (90%), and TiO₂ (88%). From these results, it is suggested that La, Ce, and Eu dopants can improve the properties of TiO₂ as well as its ability to remove cyanide species from aqueous solutions.

Comparative Study of the Effect of Doping ZnTiO3 with Rare Earths (La and Ce) on the Adsorption and Photodegradation of Cyanide in Aqueous Systems

Cyanide is a highly toxic compound that can pose serious health problems to both humans and aquatic organisms. Therefore, the present comparative study focuses on the removal of total cyanide from aqueous solutions by photocatalytic adsorption and degradation methods using ZnTiO₃ (ZTO), La/ZnTiO₃ (La/ZTO), and Ce/ZnTiO₃ (Ce/ZTO). The nanoparticles were synthesized by the sol-gel method and characterized by X-ray powder diffractometry (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), Diffuse reflectance spectroscopy (DRS), and Specific surface area (SSA). The adsorption equilibrium data were fitted to the Langmuir and Freundlich isotherm models. Adsorption kinetics were also evaluated using the pseudo-first-order and pseudo-second-order models and the intraparticle diffusion model. Likewise, the photodegradation of cyanide under simulated sunlight was investigated and the reusability of the synthesized nanoparticles for cyanide removal in aqueous systems was determined. The results demonstrated the effectiveness of doping with lanthanum (La) and cerium (Ce) to improve the adsorbent and photocatalytic properties of ZTO. In general, La/ZTO showed the maximum percentage of total cyanide removal (99.0%) followed by Ce/ZTO (97.0%) and ZTO (93.6%). Finally, based on the evidence of this study, a mechanism for the removal of total cyanide from aqueous solutions using the synthesized nanoparticles was proposed.