New mechanistic insight into rapid adsorption of pharmaceuticals from water utilizing activated biochar

Synthesis of recyclable and light-weight graphene oxide/chitosan/genipin sponges for the adsorption of diclofenac, triclosan, and microplastics

Emerging micropollutants, such as pharmaceuticals and microplastics (MPs), have become a pressing water environmental concern. The aim of this study is to synthesize chitosan sponges using graphene oxide (GO) and genipin (GP) for the removal of pharmaceuticals (diclofenac (DCF) and triclosan (TCS)) and MPs, verify their adsorption mechanisms, evaluate the effects of temperature, pH, and salinity on their adsorption capacities, and determine their reusability. The GO5/CS/GP sponge exhibited a macroporous nature (porosity = 95%, density = 32.6 mg/cm3). GO and cross-linker GP enhanced the adsorption of DCF, TCS, and polystyrene (PS) MPs onto the CS sponges. The adsorption of DCF, TCS, and PS MPs involved multiple steps: surface diffusion and pore diffusion of the sponge. The adsorption isotherms demonstrated that Langmuir model was the most fitted well model to explain adsorption of TCS (qm = 7.08 mg/g) and PS MPs (qm = 7.42 mg/g) on GO5/CS/GP sponge, while Freundlich model suited for DCF adsorption (qm = 48.58 mg/g). DCF adsorption was thermodynamically spontaneous and endothermic; however, the adsorption of TCS and PS MPs was exothermic (283-313 K). The optimal pH was 5.5-7 due to the surface charge of the GO5/CS/GP sponge (pHzpc = 5.76) and ionization of DCF, TCS, and PS MPs. As the salinity increased, DCF removal efficiency drastically decreased due to the weakening of electrostatic interactions; however, TCS removal efficiency remained stable because TCS adsorption was mainly caused by hydrophobic and π-π interactions rather than electrostatic interaction. The removal of PS MPs was enhanced by the electrostatic screening effects of high Na+ ions. PS nanoplastics (average size = 26 nm) were removed by the GO5/CS/GP sponge at a rate of 73.0%, which was better than that of PS MPs (41.5%). In addition, the GO5/CS/GP sponge could be recycled over five adsorption-desorption cycles.

Characteristics of hydrogen energy yield in steam gasification of coffee residues

Coffee residues (CRs) were gasified using a laboratory-scale fluidized bed gasifier with an air/steam mixture as the carrier gas. The gasification was conducted at an equivalence ratio (ER) of 0.3, and different operation temperatures (700, 800, and 900 °C) and steam-to-biomass (S/B) ratios (0, 0.75, and 1.5) were applied. Increasing temperature without steam boosted H2 and CO concentrations in producer gas, raising lower heating value (LHV) and cold gas efficiency (CGE) through endothermic reactions like Boudouard, tar cracking, and water-gas formation. At 900 °C, gas had LHV of 3.76 MJ/Nm3 and CGE of 22.47%. It was elevating temperature from 700 to 900 °C and S/B ratio to 1.5 raised H2 and CO concentrations from 2.04 to 8.60% and from 9.56 to 11.8%, respectively. This also increased LHV from 2.23 to 3.89 MJ/Nm3 and CGE from 11.28 to 25.08%. The steam gasification reaction was found to increase the H2 concentration and was thus considered effective in converting CRs to syngas and increasing energy production. Overall, the study successfully demonstrated the feasibility of steam gasification as a means of converting coffee residues to syngas and increasing energy production. The results also highlighted the importance of operating temperature and S/B ratio in improving the gasification process.

Dual valorization of coastal biowastes for tetracycline remediation and biomethane production: A composite assisted anaerobic digestion

Harnessing coastal biowaste for dual valorization in water treatment and biofuel production holds paramount importance for sustainability and resource challenges. This study investigated the potential of engineered composite (CABC) derived from coastal biowaste-based materials for tetracycline (TC) removal and biomethane production. High-yield calcium carbonate (CaCO3; 95.65%; bivalve shells) and biochar (GA-BC; 41.50%; green macroalgae) were produced and used as precursors for CABC. The characterization results revealed presence of β-CaCO3 and ν2-CO3 aragonite in CaCO3, and composite homogeneity was achieved. The CABC exhibited a maximum TC sorption capacity of 342.26 mg/g via synergistic sorption mechanisms (i.e., surface/pore filling, electrostatic attraction, calcium ion exchange, and chelation). Supplementation of anaerobic digestion process with GA-BC, CaCO3, and CABC was investigated via three consecutive cycles. Biochemical methane potential of glucose as a sole substrate was increased from 157.50 to 217.00, 187.00, and 259.00 mL-CH4, while dual substrate (glucose+TC) treatment was increased from 94.5 to 146.5, 129.0, and 153.00 mL-CH4 for GA-BC, CaCO3, and CABC, respectively. Moreover, system stability and TC removal were increased with the addition of GA-BC (40.90%), CaCO3 (16.30%), and CABC (53.70%). Therefore, this study exemplifies the circular bioeconomy approach, demonstrating the sustainable use of biowaste-derived composite for water treatment and biofuel production.

Rice husk hydrochar prepared by hydrochloric acid assisted hydrothermal carbonization for levofloxacin removal in bioretention columns

Hydrochars are promising adsorbents in pollutant removal for water treatment. Herein, hydrochloric acid (HCl) co-hydrothermally treated hydrochars were prepared from rice husk biomass at 180 °C via a one-step hydrothermal method. Adsorption behaviors of levofloxacin (LVX) on hydrochars were evaluated. The specific surface area and pore volume of the hydrochar synthesized in 5 mol/L HCl (5H-HC) were almost 17 and 8 times of untreated hydrochar, respectively. The 5H-HC sample exhibited the highest LVX adsorption capability at room temperature (107 mg/g). Thermodynamic experimental results revealed that adsorption was a spontaneous endothermic process. Yan model provided the best description of the breakthrough behavior of LVX in bioretention column, indicating that the adsorption on the samples involved several rate-limiting factors including diffusion and mass transfer. The results show that facile HCl co-hydrothermal carbonization of waste biomass can produce novel hydrochars with high LVX adsorption ability.

Synergistic mechanisms for the superior sorptive removal of aquatic pollutants via functionalized biochar-clay composite

This study investigated the successful synthesis of functionalized algal biochar-clay composite (FBKC). Subsequently, the sorption performance of FBKC towards norfloxacin (NFX) antibiotic and crystal violet dye (CVD) from water was extensively assessed in both batch and continuous flow systems. A series of characterization techniques were carried out for FBKC and the utilized precursors, indicating that the surface area of FBKC was increased thirty-fold with a well-developed pore structure compared to the original precursors. FBKC demonstrated a maximum sorption capacity of 192.80 and 281.24 mg/g for NFX and CVD, respectively. The suited fitting of the experimental data to Freundlich and Clark models suggested multi-layer sorption of NFX/CVD molecules. The mechanistic studies of NFX/CVD sorption onto FBKC unveiled multiple mechanisms, including π-π interaction, hydrogen bonding, electrostatic attraction, and surface/pore filling effect. The estimated cost of 5.72 €/kg and superior sorption capacity makes FBKC an efficient low-cost sorbent for emergent water pollutants.

Application of conventional and emerging low-cost adsorbents as sustainable materials for removal of contaminants from water

The impact of water pollution has led to the search for cost-effective and environmentally friendly treatment processes to alleviate the associated environmental hazards. Adsorption is identified as an advanced treatment technology that offers simplicity and cheap alternatives to water treatment technologies when low-cost adsorbents such as industrial by-products, waste, and agricultural waste are utilized. The utilization of these materials as low-cost adsorbents for the treatment of drinking water will bring them some value. Several practices have been done to improve the removal efficiencies of the low-cost adsorbents in order to achieve WHO standards of drinking water quality. The paper highlights some of the synthesis routes employed for the modification of low-cost adsorbents. This updated review provides information on the different applications of low-cost adsorbents in removing pollutants and their adsorption capacities in an attempt to deploy the recent sustainable low-cost adsorbents with high removal efficiencies for water treatment. Future research should focus on the fabrication of hybrid low-cost adsorbents with multifunctional and antimicrobial properties. In addition, life cycle assessment (LCA) should be conducted to reveal the environmental burdens associated with the modification of the low-cost adsorbent to improve their removal efficiencies.

Anomalously abrupt switching of wurtzite-structured ferroelectrics: simultaneous non-linear nucleation and growth model

Ferroelectric polarization switching is one common example of a process that occurs via nucleation and growth, and understanding switching kinetics is crucial for applications such as ferroelectric memory. Here we describe and interpret anomalous switching dynamics in the wurtzite-structured nitride thin film ferroelectrics Al0.7Sc0.3N and Al0.94B0.06N using a general model that can be directly applied to other abrupt transitions that proceed via nucleation and growth. When substantial growth and impingement occur while nucleation rate is increasing, such as in these wurtzite-structured ferroelectrics under high electric fields, abrupt polarization reversal leads to very large Avrami coefficients (e.g., n = 11), inspiring an extension of the KAI (Kolmogorov-Avrami-Ishibashi) model. We apply this extended model to two related but distinct scenarios that crossover between (typical) behavior described by sequential nucleation and growth and a more abrupt transition arising from significant growth prior to peak nucleation rate. This work therefore provides a more complete description of general nucleation and growth kinetics applicable to any system while specifically addressing the anomalously abrupt polarization reversal behavior in new wurtzite-structured ferroelectrics.

Sustainable functionalized smectitic clay-based nano hydrated zirconium oxides for enhanced levofloxacin sorption from aqueous medium

In this study, the functionalized smectitic clay (SC)-based nanoscale hydrated zirconium oxide (ZrO-SC) was successfully synthesized and utilized for the adsorptive removal of levofloxacin (LVN) from an aqueous medium. The synthesized ZrO-SC and its precursors (SC and hydrated zirconium oxide (ZrO(OH)₂)) were extensively characterized using various analytical methods to get insight into their physicochemical properties. The results of stability investigation confirmed that ZrO-SC composite is chemically stable in strongly acidic medium. The surface measurements revealed that ZrO impregnation to SC resulted in an increased surface area (six-fold higher than SC). The maximum sorption capacity of ZrO-SC for LVN was 356.98 and 68.87 mg g^-1 during batch and continuous flow mode studies, respectively. The mechanistic studies of LVN sorption onto ZrO-SC revealed that various sorption mechanisms, such as interlayer complexation, π-π interaction, electrostatic interaction, and surface complexation were involved. The kinetic studies of ZrO-SC in the continuous-flow mode indicated the better applicability of Thomas model. However, the good fitting of Clark model suggested the multi-layer sorption of LVN. The cost estimation of the studied sorbents was also assessed. The obtained results indicate that ZrO-SC is capable of removing LVN and other emergent pollutants from water at a reasonable cost.

A comprehensive review on sustainable clay-based geopolymers for wastewater treatment: circular economy and future outlook

In the present era of significant industrial development, the presence and dispersal of countless water contaminants in water bodies worldwide have rendered them unsuitable for various forms of life. Recently, the awareness of environmental sustainability for wastewater treatment has increased rapidly in quest of meeting the global water demand. Despite numerous conventional adsorbents on deck, exploring low-cost and efficient adsorbents is interesting. Clays and clays-based geopolymers are intensively used as natural, alternative, and promising adsorbents to meet the goals for combating climate change and providing low carbon, heat, and power. In this narrative work, the present review highlights the persistence of some inorganic/organic water pollutants in aquatic bodies. Moreover, it comprehensively summarizes the advancement in the strategies associated with synthesizing clays and their based geopolymers, characterization techniques, and applications in water treatment. Furthermore, the critical challenges, opportunities, and future prospective regarding the circular economy are additionally outlined. This review expounded on the ongoing research studies for leveraging these eco-friendly materials to address water decontamination. The adsorption mechanisms of clays-based geopolymers are successfully presented. Therefore, the present review is believed to deepen insights into wastewater treatment using clays and clays-based geopolymers as a groundbreaking aspect in accord with the waste-to-wealth concept toward broader sustainable development goals.

Preparation of Biochar with Developed Mesoporous Structure from Poplar Leaf Activated by KHCO3 and Its Efficient Adsorption of Oxytetracycline Hydrochloride

The effective removal of oxytetracycline hydrochloride (OTC) from the water environment is of great importance. Adsorption as a simple, stable, and cost-effective technology is regarded as an important method for removing OTC. Herein, a low-cost biochar with a developed mesoporous structure was synthesized via pyrolysis of poplar leaf with potassium bicarbonate (KHCO₃) as the activator. KHCO₃ can endow biochar with abundant mesopores, but excessive KHCO₃ cannot continuously promote the formation of mesoporous structures. In comparison with all of the prepared biochars, PKC-4 (biochar with a poplar leaf to KHCO₃ mass ratio of 5:4) shows the highest adsorption performance for OTC as it has the largest surface area and richest mesoporous structure. The pseudo-second-order kinetic model and the Freundlich equilibrium model are more consistent with the experimental data, which implies that the adsorption process is multi-mechanism and multi-layered. In addition, the maximum adsorption capacities of biochar are slightly affected by pH changes, different metal ions, and different water matrices. Moreover, the biochar can be regenerated by pyrolysis, and its adsorption capacity only decreases by approximately 6% after four cycles. The adsorption of biochar for OTC is mainly controlled by pore filling, though electrostatic interactions, hydrogen bonding, and π-π interaction are also involved. This study realizes biomass waste recycling and highlights the potential of poplar leaf-based biochar for the adsorption of antibiotics.

Trends in removal of pharmaceuticals in contaminated water using waste coffee and tea-based materials with their derivatives

The introduction of large amounts of pharmaceuticals into the environmental waters is well-documented in literature with their occurrence reported in all different water matrices accessible to humans and animals. At the same time, the increasing consumption of coffee and tea-based beverages results in the generation of solid waste, which is mostly disposed-off in the environment. To minimize environmental pollution, coffee and tea-based materials have been proposed as suitable options to remove pharmaceuticals in environmental waters. Therefore, this article provides a critical review on the preparation and applications of coffee and tea-based materials in removing pharmaceuticals from contaminated water. In this context, most studies in literature focused on the applications of these materials as adsorbents, while only limited work on their role in degradation of pharmaceuticals is discussed. The successful application in adsorption studies is attributed to high surface areas of adsorbents and the ability to easily modify the adsorbent surfaces by incorporating functional groups that provide additional oxygen atoms, which promote easy interactions with pharmaceuticals. Hence, the adsorption mechanisms are mostly described by hydrogen bonding, electrostatic and π-π interactions with sample pH playing a dominant role in the adsorption process. Overall, the present article focused on the developments, trends and future research direction on the preparations and applications of coffee and tea-based materials for efficient removal of pharmaceuticals in water. PRACTITIONER POINTS: Review of tea and coffee wastes application for removal of pharmaceuticals in water Key applications in adsorption and degradation of pharmaceuticals in water Removal mostly explained by hydrogen bonding, electrostatic, and π-π interactions Trends, gaps, and future research to be explored are reviewed and highlighted.

Evaluation insight into Abu Zenima clay deposits as a prospective raw material source for ceramics industry: Remote Sensing and Characterization

The rapid development and mutations have heightened ceramic industrialization to supply the countries' requirements worldwide. Therefore, the continuous exploration for new reserves of possible ceramic-raw materials is needed to overwhelm the increased demand for ceramic industries. In this study, the suitability assessment of potential applications for Upper Cretaceous (Santonian) clay deposits at Abu Zenima area, as raw materials in ceramic industries, was extensively performed. Remote sensing data were employed to map the Kaolinite-bearing formation as well as determine the additional occurrences of clay reserves in the studied area. In this context, ten representative clayey materials from the Matulla Formation were sampled and examined for their mineralogical, geochemical, morphological, physical, thermal, and plasticity characteristics. The mineralogical and chemical compositions of starting clay materials were examined. The physicochemical surface properties of the studied clay were studied utilizing SEM-EDX and TEM. The particle-size analysis confirmed the adequate characteristics of samples for white ceramic stoneware and ceramic tiles manufacturing. The technological and suitability properties of investigated clay deposits proved the industrial appropriateness of Abu Zenima clay as a potential ceramic raw material for various ceramic products. The existence of high kaolin reserves in the studied area with reasonable quality and quantity has regional significance. It would significantly help reduce the manufacturing cost and overwhelm the high consumption rate. The ceramic manufacturers in the investigated areas are expected to bring steady producers into the industry in the long term to gain the advantage of low-cost raw materials, labor, and factory construction.

Tuning cationic/anionic dyes sorption from aqueous solution onto green algal biomass for biohydrogen production

Global water security and energy demands associated with uncontrollable population growth and rapid industrial progress are one of the utmost serious needs dangerously confronting humanity. On account of waste as a wealth strategy; a multifunctional eco-friendly sorbent (MGAP) from green alga was prepared successfully for remediation of cationic/anionic organic dyes and biohydrogen production. The structural and morphological properties of sorbent were systematically scrutinized by a variety of spectral analyses. The loading capacity of MGAP towards rhodamine B (RhB) and methyl orange (MO) dyes was inclusivity inspected under variable experimental conditions. The adsorption kinetics of both dyes onto MGAP was in good agreement with pseudo-second-order theory, whereas adsorption isotherms could fit well with the Langmuir model, with satisfactory loading capacities of 144.92 and 196.04 mg g^-1 for RhB and MO molecules, respectively. Moreover, ultra-sonication treatment admirably decreased the sorption equilibrium time from 180.0 min to 30.0 min. Furthermore, spent sorbent was managed particularly for biohydrogen production with a measured yield of 112.89, 116.59, and 128.17 mL-H₂/gVS for MGAP, MGAP-MO, and MGAP-RhB, respectively. Overall, the produced MGAP can potentially be offered up as a promising dye scavenger for wastewater remediation and biohydrogen production, thereby fulfilling waste management and circular economy.

Temperature Effect on Ionic Polymers Removal from Aqueous Solutions Using Activated Carbons Obtained from Biomass

The main aim of this study was the determination of temperature influence on adsorption mechanisms of anionic poly(acrylic acid) (PAA) and cationic polyethylenimine (PEI) on the surface of activated carbons (AC) obtained via chemical activation of nettle (NE) and sage (SA) herbs. All measurements were performed at pH 3 at three temperature values, i.e., 15, 25 and 35 °C. The adsorption/desorption of these polymers from single and mixed solution of adsorbates was also investigated. The viscosity studies were additionally performed to obtain hydrodynamic radius values characterizing polymeric macromolecules conformation in the solution. These data are very important for the explanation of changes of linear dimensions of polymer chains with the rise of temperature caused by the modification of polymer-solvent interactions. Moreover, the XPS studies for the systems showing the highest adsorbed amounts in the specific temperature conditions were carried out. These were the systems containing PEI, PAA and NE-AC activated carbon at 25 °C. In such a case, the maximum adsorption capacity towards PAA macromolecules from a single solution of adsorbate reaches the value of 198.12 mg/g. Additionally, the thermodynamic parameters including the free energies of adsorption, as well as changes in free enthalpy and entropy were calculated.

Biochar-mediated removal of pharmaceutical compounds from aqueous matrices via adsorption

Pharmaceutical is one of the noteworthy classes of emerging contaminants. These biologically active compounds pose a range of deleterious impacts on human health and the environment. This is attributed to their refractory behavior, poor biodegradability, and pseudopersistent nature. Their large-scale production by pharmaceutical industries and subsequent widespread utilization in hospitals, community health centers, and veterinary facilities, among others, have significantly increased the occurrence of pharmaceutical residues in various environmental compartments. Several technologies are currently being evaluated to eliminate pharmaceutical compounds (PCs) from aqueous environments. Among them, adsorption appears as the most viable treatment option because of its operational simplicity and low cost. Intensive research and development efforts are, therefore, currently underway to develop inexpensive adsorbents for the effective abatement of PCs. Although numerous adsorbents have been investigated for the removal of PCs in recent years, biochar-based adsorbents have garnered tremendous scientific attention to eliminate PCs from aqueous matrices because of their decent specific surface area, tunable surface chemistry, scalable production, and environmentally benign nature. This review, therefore, attempts to provide an overview of the latest progress in the application of biochar for the removal of PCs from wastewater. Additionally, the fundamental knowledge gaps in the domain knowledge are identified and novel strategic research guidelines are laid out to make further advances in this promising approach towards sustainable development.

Removal of nutrients from pulp and paper biorefinery effluent: Operation, kinetic modelling and optimization by response surface methodology

This study investigated the effectiveness of extended aeration system (EAS) and rice straw activated carbon-extended aeration system (RAC-EAS) in the treatment of pulp and paper biorefinery effluent (PPBE). RAC-EAS focused on the efficient utilization of lignocellulosic biomass waste (rice straw) as a biosorbent in the treatment process. The experiment was designed by response surface methodology (RSM) and conducted using a bioreactor that operated at 1-3 days hydraulic retention times (HRT) with PPBE concentrations at 20, 60 and 100%. The bioreactor was fed with real PPBE having initial ammonia-N and total phosphorus (TP) concentrations that varied between 11.74 and 59.02 mg/L and 31-161 mg/L, respectively. Findings from the optimized approach by RSM indicated 84.51% and 91.71% ammonia-N and 77.62% and 84.64% total phosphorus reduction in concentration for EAS and RAC-EAS, respectively, with high nitrification rate observed in both bioreactors. Kinetic model optimization indicated that modified stover models was the best suited and were statistically significant (R² ≥ 0.98) in the analysis of substrate removal rates for ammonia-N and total phosphorus. Maximum nutrients elimination was attained at 60% PPBE and 48 h HRT. Therefore, the model can be utilized in the design and optimization of EAS and RAC-EAS systems and consequently in the prediction of bioreactor behavior.

Synthesis of biochar from iron-free and iron-containing microalgal biomass for the removal of pharmaceuticals from water

The contamination of natural water bodies with pharmaceutical compounds has raised significant concerns about ecological and public health safety. In this study, biochars were synthesized from iron-free microalgal biomass (harvested by centrifugation) and iron-containing microalgal biomass (harvested by coagulation) and tested for the adsorption of ciprofloxacin (CIP) and diclofenac (DIC) from water in batch and fixed-bed column continuous studies. The physicochemical properties of synthesized biochars were analyzed using Brunauer, Emmett and Teller (BET) surface area analyzer, elemental analyzer, Fourier Transformed Infrared spectroscopy (FTIR), X-ray Diffractometer (XRD), and Scanning electron microscope with energy dispersive spectroscopy (SEM-EDS). The maximum monolayer adsorption capacities of iron-containing biochar (FBC750W) and iron-free biochar (MBC750W) based on the Langmuir model were obtained as 75.97 mg/g and 39.08 mg/g for CIP, and 40.99 mg/g and 6.77 mg/g for DIC, respectively. Comparatively, maximum monolayer adsorption capacities of commercial activated carbon (C-AC) were found to be 50.97 mg/g and 46.39 mg/g for CIP and DIC, respectively. In fixed-bed column continuous adsorption studies, the effects of flow rate (1 and 2 mL/min) and the adsorbent amount (50 and 100 mg) on adsorption performance were evaluated. Column kinetic models, such as Bohart-Adams model and Fractal-like Bohart-Adams model were examined. The adsorption mechanisms were proposed as pore filling, π-π interaction, and electrostatic interaction. Overall, the results of this study revealed that microalgal biomass, harvested with FeCl₃, can be used for the direct synthesis of iron-containing biochar for the removal of pharmaceuticals from water.

Novel GO/Fe-Mn hybrid for the adsorptive removal of Pb(II) ions from aqueous solution and the spent adsorbent disposability in cement mix: compressive properties and leachability study for circular economy benefits

GO/Fe-Mn hybrids were prepared by a single-pot chemical precipitation method and were characterized using FTIR, XRD, Raman, zeta potential, and FESEM, which confirmed the impregnation of Fe/Mn onto GO sheets. The synthesized hybrids were successively applied in removing the Pb(II) ions from aqueous solution and later utilizing the spent adsorbent to increase the properties of cement. The adsorption capability of the synthesized hybrid was seen in a set of batch studies to find out that about 15 min of contact time was required to remove 99% of the contaminant at a pH of 5 ± 0.2 and a dose of 0.83 g/L. The mechanism of the adsorption process for the synthesized hybrid was well described by Elovich kinetic model with an R² of 0.99 and Langmuir isotherm model, also with an R² of 0.99. The desorption studies conducted using 0.1 M HCl solution showed significant stability of the hybrid with a drop of 12% in the removal efficiency of Pb after up to five adsorption-desorption cycles. This points to an efficient adsorbent having potential for economical use. Later, the spent adsorbent was mixed with cement at ratios of 0.05%, 0.1%, and 0.5%, and compressive strength tests were performed, which showed an increase in the strength by 7.62%, 16.11%, and 26.82% at 28 days of curing time. The TCLP and SPLP tests performed on the hybrid and cement-spent adsorbent mix showed all the leaching parameters were well within the permissible limits. This development shows the potential for the use of spent adsorbent in a circular economy model.

Activated Biocarbons Obtained from Plant Biomass as Adsorbents of Heavy Metal Ions

This paper deals with the adsorption of heavy metal ions on the surface of carbonaceous materials obtained via the chemical activation of biomass. Waste plum stones, pine sawdust and horsetail herb were used as the precursors of carbonaceous adsorbents. The effect of the precursor type and preparation procedure on the physicochemical properties of activated biocarbons and their sorption abilities towards Pb(II) and Cu(II) ions have been checked. The obtained micro-mesoporous activated biocarbons were characterized by determination of elemental composition and ash content, the number of surface functional groups and pH of water extracts as well as textural study based on low temperature nitrogen adsorption/desorption and scanning electron microscopy. Additionally, the electrokinetic studies including solid surface charge density and zeta potential determination were performed. Moreover, the adsorption data modelling (equilibrium and kinetics), XPS results analysis and comparison of parameters characterizing electrical double layer formed at the solid-liquid interface enabled the specification of the mechanism of heavy metals binding with the activated biocarbons surface. The maximum adsorption capacity towards copper and lead ions (177.5 and 178.1 mg/g, respectively) was found for plum stone-based activated biocarbon. For all carbonaceous materials, better fit to the experimental data was achieved with a Langmuir isotherm than a Freundlich one. In turn, a better fit of the kinetics data was obtained using the pseudo-second order model.

The potential of biochar-photocatalytic nanocomposites for removal of organic micropollutants from wastewater

Biochar (BC)-photocatalyst nanocomposites have emerged as appealing water and wastewater treatment technology. Such nanocomposite materials benefit from the synergistic effect of adsorption and photocatalysis to attain improved removal of pollutants from water and wastewater. Under this review, three BC-based nanocomposite photocatalysts such as BC-TiO₂, BC-ZnO, and BC-spinel ferrites were considered. These nanocomposites acquire intrinsic properties to improve the practical limitations of the pristine BC and photocatalysts. The BC-based nanocomposites attained high photocatalytic activity, mechanical hardness, thermal stability, chemically non-reactive, magnetically permeable, reduced energy band gaps, improved reusability, and simplified recovery. Moreover, BC-based photocatalytic nanocomposites showed reduced recombination rates of the electron-hole pairs which are desirable for photocatalytic applications. However, the surface areas of the composites are usually smaller than that of the BC but higher than those of the pristine photocatalysts. Practically, the performances of the nanocomposites are much superior to those of the corresponding pristine components. This hybrid treatment technology is an emerging field and its industrial application is still at an early stage of the investigation. Therefore, exploring the full potential and practical applications of this technology is highly encouraging. Hence, this review focused on the critical evaluation of the most recent research on the synthesis, characterization, and photocatalytic treatment efficiency of the BC photocatalyst nanocomposites towards emerging pollutants in the aqueous medium. Moreover, the influence of various sources of BC feedstocks and their limitations on adsorption and photodegradation activities are discussed in detail. Finally, concluding remarks and future research directions are given to assist and shape the exploration of BC-based nanocomposite photocatalysts in water treatment.

Fabrication of Pd/Sludge-biochar electrode with high electrochemical activity on reductive degradation of 4-chlorophenol in wastewater

Effective treatment and utilization of sludge contribute to achieve conventional carbon emission reduction and resource recovery, which is of great significance to realize carbon neutralization of WWTPs. Sludge carbonization derived biochar has attracted more interest because of high potential as catalytic materials. Therein, sludge-derived electrode exhibits a promising potential in the case of sludge utilization for electrocatalysis, however, electrocatalytic performance of the already reported sludge-derived electrode is unsatisfactory due to insufficient active sites. In this study, an efficient Pd/sludge-biochar loaded foam nickel (Pd-SAC@Ni) was successfully fabricated using simple pyrolysis and solidification method, and exhibited remarkable electrocatalytic performance for 4-chlorophenol (4-CP) degradation. Furthermore, the morphology, element distribution and crystal composition were characterized by SEM, EDS, XPS and XRD. The Pd-SAC@Ni electrode exhibited superior electrocatalytic performance than Ni, SAC@Ni, Pd-Ni electrodes. The reduction rate of 98.9% was achieved at current density of 5 mA cm^-2, 4-CP concentration of 0.8 mM and initial pH of 7.0. Also, Pd-SAC@Ni electrode showed desirable reusability and achieved 98% of 4-CP removal after multiple runs of experiments. Moreover, the active hydrogen species (H*) generation capacity of electrodes was determined using tert-butanol (TBA) as trapping agent. The mechanism analysis demonstrated that direct reduction process and indirect reduction process both involved in the 4-CP degradation process, and their contribution were 19.5% and 80.5%, respectively. Then, the intermediates formed in the electrochemical degradation of 4-CP were revealed by HPLC and the plausible degradation pathway was proposed. This study provides a cost-effective approach for preparing sludge biochar electrode, and explored a novel way to promote resourceful utilization of sludge for carbon neutrality.

Comparative study on characteristics and mechanism of levofloxacin adsorption on swine manure biochar

This study evaluated the relationship between pyrolysis temperature (300-900 ℃), characteristics of swine manure (SM)-derived biochar (BC), and its adsorption of levofloxacin (LEV). The surface structure and chemistry of SM-derived BCs were characterized using Brunauer-Emmett-Teller analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. According to the characteristic analysis, the surface area and graphitization degree of SM-derived BC increased as temperature rose. The highest adsorption capacity was achieved by BC-900 (158 mg/g); this level was higher than that achieved in previous studies and comparable to that of commercial activated carbons. Characterization and adsorption experiments indicated that pore-filling, π-π stacking interaction, π-π electron donor-acceptor, H-bonding, and hydrophobic interactions each played a critical role in the adsorption of LEV on SM-derived BC. Collectively, this study confirms the potential utility of SM-derived BC for the removal of antibiotics.

Synthesis and Characterization of a Magnetic Carbon Nanofiber Derived from Bacterial Cellulose for the Removal of Diclofenac from Water

Engineering and synthesis of novel materials are vital for removing emerging pollutants, such as pharmaceuticals from contaminated water. In this study, a magnetic carbon nanofiber (MCF) fabricated from bacterial cellulose was tested for the adsorption of diclofenac from water. The physical and chemical properties of the synthesized adsorbent were examined by field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, energy-dispersive X-ray spectroscopy (EDS), a vibrating sample magnetometer (VSM), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The characterization results showed that the MCF is a carbon nanofiber with a three-dimensional interconnect network, forming a porous material (mesopores and macropores) with a specific surface area of 222.3 m²/g. The removal of diclofenac (10 mg/L) by the MCF (0.75 g/L) was efficient (93.2%) and fast (in 20 min). According to the Langmuir isotherm model fitting, the maximum adsorption capacity of the MCF was 43.56 mg/g. Moreover, continuous adsorption of diclofenac onto MCF was investigated in a fixed-bed column, and the maximum adsorption capacity was found to be 67 mg/g. The finding of this research revealed that the MCF could be a promising adsorbent used to remove diclofenac from water, while it can be easily recovered by magnetic separation.

Critical review on adsorptive removal of antibiotics: Present situation, challenges and future perspective

This review gives a proper dedicated understanding of the contamination level, sources, and biological dangers related with different classes of antibiotics in consumable water. The literature on the adsorption of antibiotics is relatively uncommon and developments are still under progression, especially for adsorbents other than activated carbon. Also, adsorption technique has already been applied vastly for water treatment. Notwithstanding significant progressions, designed natural wastewater treatment frameworks are just bearably effective (48-77%) in the expulsion of antibiotics. Hence, the compilation of available literature especially for antibiotic adsorption was much needed. Moreover, the conventional adsorbents have some limitations of their own. In this study, the main focus was laid on unconventional adsorbents such as Biochar, Biopolymers, Carbon Nanotubes, Clays, Metal-Organic Frameworks, Microalgae and some miscellaneous adsorbents. The mechanism of adsorption by the unconventional adsorbents includes electrostatic interactions, π-π bonding, weak Van der Waal forces, H-bonding and surface complexation, which was similar to that of conventional adsorbents and hence these unconventional adsorbents can easily replace the costlier conventional adsorbents with even better adsorption efficiency. This paper also briefly discussed the thermodynamics, adsorption equilibrium; isotherm and kinetics of adsorption. This review paper seizes the critical advances of adsorption phenomenon at various interfaces and lays the foundation for current scenario associated with further progress. Besides, this study would help in understanding the antibiotic adsorption, cost estimation and future goals that will attract the young the researchers of this field.

Kinetic and isotherm insights of Diclofenac removal by sludge derived hydrochar

Recently, hydrothermal carbonization emerges as the most viable option for the management of solid waste with high moisture content. Sludge derived hydrochar is used as an adsorbent for emerging contaminants or micro-pollutants in the domain of sustainability. Current study demonstrates the KOH activation of hydrochar produced from paper board mill sludge and evaluates its removal potential of a Non-steroidal anti-inflammatory drug, Diclofenac from aqueous solution. The activated hydrochars exhibited porous, spherical micro-structures with higher fraction of oxygenated functional groups paving way for the efficient adsorption of Diclofenac. The effect of initial Diclofenac concentration and contact time was ascertained using adsorption kinetics and isotherms. The adsorption kinetics exhibited second-order reaction for all adsorbents indicating higher coefficient of determination (R² > 0.9). The Diclofenac adsorption on hydrochars followed Langmuir isotherm model with the post-activated hydrochar recording a highest adsorption capacity of 37.23 mg g⁻¹ in 40 mg L⁻¹ initial Diclofenac concentration at 15 h equilibrium time.