Green Adsorbents for Wastewaters: A Critical Review

A state-of-the-art review of metal oxide nanoflowers for wastewater treatment: Dye removal

Dye wastewater consists of high solids concentrations, heavy metals, minor contaminants, dissolved chemical oxygen demand, and microorganisms. Nanoflowers are nanoparticles that resemble flowers when viewed at a microscopic level. Inorganic metal oxide nanoflowers have been discovered to be a potential source for overcoming this situation. Their flower-like features give them a higher surface area to volume ratio and porosity structure, which can absorb a significant amount of dye. The metal oxide nanoflower synthesized from different synthesis methods is used to compare which one is cost-effective and capable of generating a large scale of nanoflower. This review has demonstrated outstanding dye removal efficiency by applying inorganic nanoflowers to dye removal. Since both adsorption and photocatalytic reactions enhance the dye degradation process, complete dye degradation could be achieved. Meanwhile, the inorganic metal oxide nanoflowers' exemplary reusability characteristics with negligible performance drop further prove that this approach is highly sustainable and may help to save costs. This review has proven the momentum of obtaining high dye removal efficiency in wastewater treatment to conclude that the metal oxide nanoflower study is worth researching.

Adsorbent based on MOF-5/cellulose aerogel composite for adsorption of organic dyes from wastewater

Industries persistently contribute to environmental pollution by releasing a multitude of harmful substances, including organic dyes, which represent a significant hazard to human health. As a result, the demand for effective adsorbents in wastewater treatment technology is steadily increasing so as to mitigate or eradicate these environmental risks. In response to this challenge, we have developed an advanced composite known as MOF-5/Cellulose aerogel, utilizing the Pampas plant as a natural material in the production of cellulose aerogel. Our investigation focused on analyzing the adsorption and flexibility characteristics of this novel composite for organic dye removal. Additionally, we conducted tests to assess the aerogel's reusability and determined that its absorption rate remained consistent, with the adsorption capacity of the MOF-5/cellulose aerogel composite only experiencing a marginal 5% reduction. Characterization of the material was conducted through XRD analysis, revealing the cubic structure of MOF aerogel particles under scanning electron microscopy. Our study unequivocally demonstrates the superior adsorption capabilities of the MOF-5/cellulose aerogel composite, particularly evident in its efficient removal of acid blue dye, as evaluated meticulously using UV-Vis spectrophotometric techniques. Notably, our findings revealed an impressive 96% absorption rate for the anionic dye under acidic pH conditions. Furthermore, the synthesized MOF-5/cellulose aerogel composite exhibited Langmuir isotherm behavior and followed pseudo-second-order kinetics during the absorption process. With its remarkable absorption efficiency, MOF-5/cellulose aerogel composites are poised to emerge as leading adsorbents for water purification and various other applications.

Cd2+ removal efficiency of activated carbon from Prosopis juliflora: Optimization of preparation parameters by the Box-Behnken Design of Response Surface Methodology

The study focuses on the preparation of activated carbon from Prosopis juliflora (PJAC) wood by pyrolysis and chemical activation. The objective is to assess its effectiveness as an adsorbent for synthesizing a composite adsorbent coating (CAC) for Cadmium (Cd2+) removal from aqueous solution. The effect of preparation factors related to Cd2+ removal efficiency was assessed. The Design of Experiments (DoE) for the adsorption of Cd2+ on the PJAC were done using the Box-Behnken Design (BBD) of the Response Surface Methodology (RSM) (Design Expert software version 11). The influence of impregnation ratio (IR), carbonization time (t), and carbonization temperature (T) on the Cd (II) percent (%) removal was evaluated. The response surface graphs in 3D were also generated for the response variable, and the higher R2 coefficient values were fitted into the polynomial quadric model. The results indicated that all the variable preparation factors were significant in the Cd2+ removal by PJAC with carbonization temperature being the most significant. At the optimum conditions i.e. impregnation ratio (1.8), carbonization temperature (595 °C) and carbonization time (174 min), the model predicted a 99.9 % Cd2+ removal efficiency while the adsorption experiment obtained a 96.7 % removal efficiency, respectively. Later, the morphological and chemical properties of the PJAC prepared with optimal parameters were analyzed using different characterization techniques including SBET, SEM-EDX, pHPZC, FTIR and XRD. The SEM images revealed a rough and porous morphological surface with an SBET of 600.4 m2/g and a near neutral pHPZC of 6.92. The XRD pattern indicated the crystalline nature of the prepared adsorbent. The pre and post adsorption FTIR spectrum of the PJAC demonstrated a distinct difference with the latter showing a reduction in peak intensity and height. These results underpin the potential of utilizing invasive plants like Prosopis Juliflora as adsorbents for heavy metal removal.

Photochemical modification of tea waste by tungsten oxide nanoparticle as a novel, low-cost and green photocatalyst for degradation of dye pollutant

So far, many adsorbents and nanocomposites have been synthesized by different methods and used to remove or degradation of dye pollutants. Nowadays, the use of natural adsorbents and their modification with simple methods based on metal oxides are of interest to many researchers. In this study, for the first time, we report the simple and low-cost modification of tea pomace waste (TPW) with tungsten oxide (WO3) based on the photochemical method as a green, cost-effective, and biodegradable photocatalyst for the degradation of Rh B dye pollutant. The results obtained from FE-SEM, EDAX, XRD, XPS, PL, BET and UV-Vis Diffusive Reflectance (DRS) analyses confirmed the successful modification of the TPW surface with WO3 (WO3/TPW). The parameters affecting the photocatalytic behavior of WO3/TPW, including the time of photochemical modification and the type of radiation on its photocatalytic activity, were carefully optimized. WO3/TPW showed excellent photocatalytic activity compared to TPW for the degradation of Rh B dye pollutant under UV light for 30 min (94 %). Finally, the effective parameters on the value of Rh B dye degradation by WO3/TPW photocatalyst including pH, adsorbent dosage, the concentration of dye pollutant, and the kinetics of the degradation process were studied. It is expected that this type of photochemical modification method and natural WO3/TPW photocatalyst will be a promising path for the synthesis, modification, and increase of the photocatalytic performance of natural adsorbents.

A review on sustainable management of biomass: physicochemical modification and its application for the removal of recalcitrant pollutants-challenges, opportunities, and future directions

Adsorption is one of the most efficient methods for remediating industrial recalcitrant wastewater due to its simple design and low investment cost. However, the conventional adsorbents used in adsorption have several limitations, including high cost, low removal rates, secondary waste generation, and low regeneration ability. Hence, the focus of the research has shifted to developing alternative low-cost green adsorbents from renewable resources such as biomass. In this regard, the recent progress in the modification of biomass-derived adsorbents, which are rich in cellulosic content, through a variety of techniques, including chemical, physical, and thermal processes, has been critically reviewed in this paper. In addition, the practical applications of raw and modified biomass-based adsorbents for the treatment of industrial wastewater are discussed extensively. In a nutshell, the adsorption mechanism, particularly for real wastewater, and the effects of various modifications on biomass-based adsorbents have yet to be thoroughly studied, despite the extensive research efforts devoted to their innovation. Therefore, this review provides insight into future research needed in wastewater treatment utilizing biomass-based adsorbents, as well as the possibility of commercializing biomass-based adsorbents into viable products.

Silk adsorbent for green and efficient removal of methylene blue from wastewater

Silk, a naturally occurring proteinaceous biopolymer with remarkable adsorbent properties, has been employed in wastewater remediation. The sericin coating, functioning as a protective barrier and rendering fibres impervious to external chemical attacks and preventing their involvement in chemical reactions, was removed using a greener alternative to harness silk as an effective adsorbent. Subsequently, the silk fibres underwent intermittent microwave degumming to extract sericin, and the fibres were utilized for the adsorptive exclusion of the hazardous methylene blue (MB) dye. The comparative batch adsorption studies (kinetics and isotherm) between raw silk fibres and degummed fibres were performed to comprehend the role of degumming on fibre adsorption efficacy by varying operating conditions, including pH, time of contact, initial adsorbate and dosage of adsorbent. The paramount adsorption capacity of raw silk was observed to be 137.08 mg g-1 and 179.14 mg g-1 for degummed silk when adsorbate conc. was 100 ppm. The kinetics of adsorption obeyed pseudo-second order suggesting that the rate controlling step is chemisorptions, and data demonstrated greatest fit to Langmuir isotherm exhibiting mono-layer adsorption. Further, biodegradability was studied by mimicking natural environmental conditions where the raw and degummed silk fibres demonstrated 51% and 53% degradation, respectively, after 180 days. Overall, based on obtained results, this study highlights the suitability of silk as an effective as well as sustainable adsorbent for the exclusion of toxic methylene blue dye from wastewater.

Environmental biotechnology and the involving biological process using graphene-based biocompatible material

Biotechnology is a promising approach to environmental remediation but requires improvement in efficiency and convenience. The improvement of biotechnology has been illustrated with the help of biocompatible materials as biocarrier for environmental remediations. Recently, graphene-based materials (GBMs) have become promising materials in environmental biotechnology. To better illustrate the principle and mechanisms of GBM application in biotechnology, the comprehension of the biological response of microorganisms and enzymes when facing the GBMs is needed. The review illustrated distinct GBM-microbe/enzyme composites by providing the GBM-microbe/enzyme interaction and the determining factors. There are diverse GBM modifications for distinct biotechnology applications. Each of these methods and applications depends on the physicochemical properties of GBMs. The applications of these composites were mainly categorized as pollutant adsorption, anaerobic digestion, microbial fuel cells, and organics degradation. Where information was available, the strategies and mechanisms of GBMs in improving application efficacies were also demonstrated. In addition, the biological response, from microbial community changes, extracellular polymeric substances changes to biological pathway alteration, may become important in the application of these composites. Furthermore, we also discuss challenges facing the environmental application of GBMs, considering their fate and toxicity in the ecosystem, and offer potential solutions. This research significantly enhances our comprehension of the fundamental principles, underlying mechanisms, and biological pathways for the in-situ utilization of GBMs.

Nanomaterials for Removal of Phenolic Derivatives from Water Systems: Progress and Future Outlooks

Environmental pollution remains one of the most challenging problems facing society worldwide. Much of the problem has been caused by human activities and increased usage of various useful chemical agents that inadvertently find their way into the environment. Triclosan (TCS) and related phenolic compounds and derivatives belong to one class of such chemical agents. In this work, we provide a mini review of these emerging pollutants and an outlook on the state-of-the-art in nanostructured adsorbents and photocatalysts, especially nanostructured materials, that are being developed to address the problems associated with these environmental pollutants worldwide. Of note, the unique properties, structures, and compositions of mesoporous nanomaterials for the removal and decontamination of phenolic compounds and derivatives are discussed. These materials have a great ability to scavenge, adsorb, and even photocatalyze the decomposition of these compounds to mitigate/prevent their possible harmful effects on the environment. By designing and synthesizing them using silica and titania, which are easier to produce, effective adsorbents and photocatalysts that can mitigate the problems caused by TCS and its related phenolic derivatives in the environment could be fabricated. These topics, along with the authors' remarks, are also discussed in this review.

The use of agro-waste-based adsorbents as sustainable, renewable, and low-cost alternatives for the removal of ibuprofen and carbamazepine from water

The occurrence of residual pharmaceuticals in the aquatic environment poses major toxicological impacts and adds to the increasing pressure on water resources. Many countries are already suffering from water scarcity, and with the burdening costs of water and wastewater treatment, the race towards innovative sustainable strategies for pharmaceutical remediation is ongoing. Out of the available treatment methods, adsorption proved to be a promising, environmentally friendly technique, particularly when efficient waste-based adsorbents are produced from agricultural residues, thus maximizing the value of wastes, minimizing production costs, and saving natural resources from depletion. Among the residual pharmaceuticals, ibuprofen and carbamazepine are heavily consumed and highly occurring in the environment. This paper aims to review the most recent literature on the application of agro-waste-based adsorbents as sustainable alternatives for the removal of ibuprofen and carbamazepine from contaminated waters. Highlights on the major mechanisms implicated in the adsorption of ibuprofen and carbamazepine are presented, and light is shed on multiple operational parameters that hold a key role in the adsorption process. This review also highlights the effects of different production parameters on adsorption efficiency and discusses many limitations currently encountered. Finally, an analysis is included to compare the efficiency of agro-waste-based adsorbents relative to other green and synthetic adsorbents.

Preparation of Breadfruit Leaf Biochar for the Application of Congo Red Dye Removal from Aqueous Solution and Optimization of Factors by RSM-BBD

In this work, biochar produced from breadfruit leaves was utilized to remove the toxic Congo red dye. XRD, FTIR, and FESEM-EDX were implemented to characterize the biochar. Response surface methodology (RSM) and the Box-Behnken design (BBD) techniques were used to evaluate Congo red’s optimum adsorption efficiency. The adsorption of Congo red was studied by varying dye concentrations (5–50 mg/L), times (30–240 min), pH (6–9), and dosages (0.5–2 g/100 mL). X-ray diffractometer results show that the structure of biochar is amorphous. The biochar exhibited unbounded OH, aliphatic CH group, and C=O stretch, as shown by the band peaks at 3340 cm−1, 2924 cm−1, and 1625 cm−1 intensities. RSM-BBD design results showed maximum removal efficiency of 99.96% for Congo red at pH 6.37, dye concentration 45 mg/L, time 105 min, and dosage 1.92 g, respectively. The adsorption of Congo red by biochar was successfully modeled using the Langmuir model and pseudo-second-order model. The biochar produced from breadfruit leaves exhibited a high adsorption capacity of 17.81 mg/g for Congo red adsorption. It suggests that the adsorption is both homogenous monolayer and physicochemical.

Biosorbent Based on Poly(vinyl alcohol)-Tricarboxi-Cellulose Designed to Retain Organic Dyes from Aqueous Media

Methylene Blue, a cationic dye, was retained from aqueous solutions using a novel biosorbent made of poly(vinyl alcohol) reticulated with tricarboxi-cellulose produced via TEMPO oxidation (OxC25). The study of the Methylene Blue biosorption process was performed with an emphasis on operational parameters that may have an impact on it (such as biosorbent concentration, pH of the aqueous media, and temperature). The current study focused on three areas: (i) the physic-chemical characterization of the biosorbent (scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX)); (ii) biosorption data modeling to determine the quantitative characteristic parameters employing three equilibrium isotherms (Langmuir, Freundlich, and Dubinin-Radushkevich-DR); and (iii) the study of temperature influence. The results of the study showed that the Langmuir model provided a good fit for the experimental data of biosorption, realizing a maximum capacity of 806.45 mg/g at 20 °C. The free energy of biosorption (E) evaluated by the DR equation was in the range of 6.48-10.86 KJ/mol. The values of the thermodynamic parameters indicated an endothermic process because the free Gibbs energy ranged from -9.286 KJ/mol to -2.208 KJ/mol and the enthalpy was approximately -71.686 KJ/mol. The results obtained encourage and motivate the further study of this biosorption process by focusing on its kinetic aspects, establishing the biosorption's controlled steps, identifying the mechanism responsible for the retention of textile dyes presented in moderate concentration in aqueous media, and studying the biosorption process in a dynamic regime with a view to applying it to real systems.

Rapid incorporation of gold nanoparticles onto graphene oxide-polymer nanofiber membranes for photothermally-accelerated water purification

This work demonstrates the rapid coating of gold nanoparticles (AuNPs) onto electrospun composite polyacrylonitrile (PAN) nanofibers containing a large amount of graphene oxide (GO) and reduced graphene oxide (rGO) for photothermally-driven applications. A modification of GO with a cationic surfactant greatly improves its loading efficiency into the PAN nanofibers, and the subsequent hydrazine treatment readily converts the integrated GO into rGO. Rapid loading of AuNPs onto these membranes results in measurably higher photothermal heating characteristics than the pristine PAN, GO-PAN, and rGO-PAN membranes under a solar-simulated light source. The light-induced heating properties are then utilized in the removal of organic dyes in an aqueous solution. While the GO-PAN and rGO-PAN membranes remove the dyes via physical adsorption, the AuNP-loaded membranes show an additional catalytic decomposition process, resulting in detectably faster removal rates. The degradation of the organic dyes is accelerated under a solar simulated light source due to the light-enhanced heating and photocatalytic properties of the integrated AuNPs. The ability to maximize the dual properties of these membranes can greatly reduce toxic organic pollutants, which can lead to the development of practical water purification systems under sunlight irradiation.

An eco-friendly removal of Cd(II) utilizing banana pseudo-fibre and Moringa bark as indigenous green adsorbent and modelling of adsorption by artificial neural network

Heavy metal-contaminated water can be effectively treated using adsorbents made from abundantly available biomass. The present investigation was carried out to adsorb Cd(II) from synthetic solution by banana pseudo-stem (BP) and Moringa oleifera stem bark (MB). Adsorption efficiencies of both adsorbents were studied in the batch reactor by conducting experiments to determine the consequences of changes of pH, adsorbent dosages, initial Cd(II) concentrations, incubation time, and temperature. The process parameters were tuned to attain the highest possible removal percentage. The characterization of the adsorbents was performed by utilizing Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) for the fresh and metal-loaded adsorbents. Atomic absorption spectroscopy (AAS) was employed to calculate the amount of Cd(II) in an aqueous solution. The experimental data were entirely consistent with the pseudo-second-order model for BP and MB. The findings of the study illustrated the better adsorption efficiency of BP-derived adsorbent (≈ 99%) at optimum conditions over the MB (≈ 97%), and the corresponding adsorption capacities were 11.98 and 7.04 mg/g, respectively. The 4 (four) well-known isotherm models were attempted both in linear and non-linear forms. BP (R² =0.995) and MB (R² =0.994) were found to be best described by the Freundlich isotherm, which was selected based on the highest R² value. In thermodynamic studies, ΔH and ΔS were calculated for both the adsorbents. Cd(II) adsorption on BP and MB was endothermic, as evidenced by the positive ΔH. Finally, the prediction of the removal percentage was made by the artificial neural network (ANN) modelling. The present work developed regionally derived waste materials which are helpful for small-scale industrial units for their waste management in an economical and sustainable way.

Clay-polymer nanocomposites for water and wastewater treatment: A comprehensive review

A majority of water pollution or contamination occurs through the discharge of effluents from industries. Wastewater treatment is crucial to protect our water sources from harmful pollutants. Therefore, a number of efforts have been made to tackle this issue by employing different techniques. Clay minerals and polymers are among these materials used extensively in wastewater treatment. While both have their own drawbacks, it is fascinating to discover that they complement each other to overcome most of their limitations. As a result, clay-polymer nanocomposites (CPNs) have been found to be highly efficient in the adsorption of pollutants from water and show promising results to be a long-term candidate for this purpose. In this paper, we discuss about different types of clay and polymers used in the preparation of CPNs. The work also focuses on the different types of clay-polymer nanocomposites, their synthesis and factors affecting their performance such as pH, temperature, contact time, pollutant concentration and adsorbent dose. In addition, the maximum adsorption capacity, mechanism and kinetics of adsorption are highlighted to assess the performance of CPNs. Various studies indicate that CPNs are only a few steps away from becoming one of the best options for wastewater treatment due to their multiple desirable properties.

Why Is the Linearized Form of Pseudo-Second Order Adsorption Kinetic Model So Successful in Fitting Batch Adsorption Experimental Data?

There is a vast amount of literature devoted to experimental studies on adsorption from liquids examining the adsorption potential of various adsorbents with respect to various solutes. Most of these studies contain not only equilibrium but also kinetic experimental data. The standard procedure followed in the literature is to fit the kinetic experimental adsorption data to some models. Typically empirical models are employed for this purpose and among them, the pseudo-first and pseudo-second order kinetic models are the most extensively used. In particular, the linear form of their integrated equations is extensively employed. In most cases, it is found that the pseudo-second order model is not only better than other models but also leads to high fitting quality. This is rather strange since there is no physical justification for such a model, as it is well accepted that adsorption kinetics is dominated by a diffusion process. In the present work, it will be shown through examples and discussion that the success of the linearized pseudo-second order model in fitting the data is misleading. Specific suggestions on appropriate adsorption data treatment are given.

Zeolites as Adsorbents and Photocatalysts for Removal of Dyes from the Aqueous Environment

This study investigated the potential of zeolites (NH₄BETA, NH₄ZSM-5, and NaY) to remove two frequently used dyes, methylene blue (MB) and rhodamine B (RB), from an aqueous environment. The removal of dyes with zeolites was performed via two mechanisms: adsorption and photocatalysis. Removal of dyes through adsorption was achieved by studying the Freundlich adsorption isotherms, while photocatalytic removal of dyes was performed under UV irradiation. In both cases, the removal experiments were conducted for 180 min at two temperatures (283 K and 293 K), and dye concentrations were determined spectrophotometrically. Additionally, after photodegradation, mineralization was analyzed as chemical oxygen demand. A computational analysis of the structures of MB and RB was performed to gain a deeper understanding of the obtained results. The computational analysis encompassed density functional theory (DFT) calculations and analysis of two quantum-molecular descriptors addressing the local reactivity of molecules. Experimental results have indicated that the considered zeolites effectively remove both dyes through both mechanisms, especially NH₄BETA and NH₄ZSM-5, due to the presence of active acidic centers on the outer and inner surfaces of the zeolite. The lowest efficiency of dye removal was achieved in the presence of NaY zeolite, which has a lower SiO₂/Al₂O₃ ratio. A more efficient reduction was completed for RB dye, which agrees with the computationally obtained information about reactivity.

Highly Efficient and Selective Capture of Pb(II) by New Crosslinked Melamine-Based Polymethyl Methacrylate for Water Treatment

Owing to the recent developments in the polymer’s properties and application, the demands for designing different structure of polymers are greater than ever. Crosslinked polymers (CPs) are a type of porous materials that have a variety of potential applications. Because of simple methods of modification of polymethyl methacrylate (PMMA), the crosslinked PMMA considers the most commonly polymeric adsorbents. A new crosslinked melamine-based polymethyl methacrylate (C-PMMA/Mel) was prepared via a polycondensation reaction between PMMA and melamine used as a crosslinking agent. Different characterization methods were carried out to investigate the molecular structures, thermal stability, and morphology. C-PMMA/Mel was applied for the adsorption behavior toward different metal cations and detected a selective to Pb(II). The evaluation of the new polymers as adsorbent against Pb(II) ion was studied using the contact time, adsorbent dose, initial concentration, and effects of pH. The adsorption efficiency of heavy metals was improved in the presence of melamine in polymeric matrix. The C-PMMA/Mel has high efficacy in the removal of ~94% of Pb at pH 6 for one hour. Noticeably, the adsorption performance of C-PMMA/Mel perfectly suited with Freundlich isotherm and the pseudo-second-order kinetic model. Additionally, the new materials showed no obvious loss in Pb(II) removal after 7 cycles.

Cellulose nanofibers/PVA blend polymeric beads containing in-situ prepared magnetic nanorods as dye pollutants adsorbents

Magnetic beads were developed from polyvinyl alcohol and different amounts of cellulose nanofibers (CNF) by in-situ preparation of iron oxide nanoparticles in an alkaline aqueous medium at room temperature. The CNF were isolated from wheat straw, whereas the magnetic nanoparticles (MNPs) precursors were simple iron salts. The complete characterization of all the obtained materials was conducted, and among some other outstanding results it showed that all the components were strongly interacting via hydrogen bonding, while the nano-rods and husks like MNPs were effectively acting as crosslinking dots. All the prepared materials had good magnetic responses, and they were able to remove not only cationic, but also anionic dye pollutants from aqueous model solutions.

Fabrication of Cross-Linked PMMA/SnO2 Nanocomposites for Highly Efficient Removal of Chromium (III) from Wastewater

In recent times, developments in polymer application properties have required the design of different polymer structures more than ever. Cross-linked polymers (CPs) could be considered a good candidate material for potential applications when used in conjunction with nanoparticles. Cross-linked polymethyl methacrylate nanocomposites are considered to be one of the most commonly polymeric adsorbents due to their varied and simple modification methods. A new class of C-PMMA/SnO_2(a–d) nanocomposites have been fabricated as surface-selective adsorbents of Cr (III) with a good yield and different loading of SnO₂ nanoparticles. The morphology, molecular structures, and thermal stability of the new cross-linked polymers were examined using a Scanning electron microscope (SEM), the Fourier Transform Infrared method (FTIR), X-ray diffraction (XRD), and Thermogravimetric Analysis (TGA). The adsorption study of C-PMMA/SnO₂ was investigated, and an efficient level of adsorption for Cr (III) cations was detected. To evaluate the potential for the new polymers to be used as adsorbents against Cr (III) ions, the contact time, the initial concentration of Cr (III), and the effects of pH were studied. The introduction of SnO₂ into the polymer network enhanced the efficiency of the adsorption of heavy metals. The C-PMMA/SnO₂ is highly efficient at removing Cr (III) ions in wastewater samples at pH 6 for one hour. The adsorption study demonstrated that the adsorption capacity of C-PMMA/SnO₂c for Cr (III) was 1.76 mg /g, and its adsorption isotherm agreed with the Langmuir adsorption model.

Recent Advances in MOF-Based Adsorbents for Dye Removal from the Aquatic Environment

The adsorptive removal of dyes from industrial wastewater using commercially available adsorbents is not significantly efficient. Metal–organic frameworks (MOFs) offer outstanding properties which can boost the separation performance over current commercial adsorbents and hence, these materials represent a milestone in improving treatment methods for dye removal from water. Accordingly, in this paper, the recent studies in the modification of MOF structures in dye removal from the aquatic environment have been discussed. This study aims to elaborate on the synthetic strategies applied to improve the adsorption efficiency and to discuss the major adsorption mechanisms as well as the most influential parameters in the adsorptive removal of dyes using MOFs. More particularly, the advanced separation performance of MOF-based adsorbents will be comprehensively explained. The introduction of various functional groups and nanomaterials, such as amine functional groups, magnetic nanoparticles, and carbon-based materials such as graphene oxide and CNT, onto the MOFs can alter the removal efficiency of MOF-based adsorbents through enhancing the water stability, dispersion in water, interactions between the MOF structure and the contaminant, and the adsorption capacity. Finally, we summarize the challenges experienced by MOF-based materials for dye removal from water and propose future research outlooks to be considered.

New silica based adsorbent material from rice straw and its in-flow application to nitrate reduction in waters: Process sustainability and scale-up possibilities

This paper shows a particular example to move to a sustainable circular economical process from valorization of rice straw ashes by developing a green synthesis for obtaining a useful sub-product. This strategy can palliate negative effects of the agriculture waste practices on the environment and also the obtained silica reduced nitrate content in waters. It is demonstrated that the silica synthesis developed at lab was scalable more than a hundred times with good results. Adsorption studies of nitrate in standards and real well waters at lab scale and scaling-up provided similar results. Adsorption values near to 15 mg/g for nitrate standards and 8.5 mg/g for well water were obtained until achieving the initial nitrate concentration. Experimental breakthrough curves fitted to Thomas model, which gave similar results for adsorption capacities. The adsorption capacity was checked with that obtained by a commercial resin, providing improved results. The method at large scale was compared with industrial traditional methods and green adsorbents.

Adsorption and recovery of lithium ions from groundwater using date pits impregnated with cellulose nanocrystals and ionic liquid

The study aims to prepare a novel low-cost and environmentally friendly adsorbent by using date pits (DP) impregnated with cellulose nanocrystals (CNCs) and ionic liquid (IL), named IL-CNC@DP. The batch adsorption of lithium onto IL-CNC@DP and DP were studied at different pH values, initial lithium concentrations, and temperatures. The thermodynamics constants of the adsorption process showed that the IL-CNC@DP was exothermic, did not favor a high level of disorder, and spontaneous in nature. At pH 6, there is a significant increase in the removal efficiency where it increased to 90%. This also could be explained by the fact that electrostatic attraction forces and hydrogen bonding existed between the protonated Li⁺ and the less protonated IL-CNC@DP adsorbent surface, which enhanced the percentage of Li⁺ removal. A strong inter- and intra-hydrogen bonding (O-H) stretching absorption is seen at 3311 cm^-1 that occurs in cellulose components. In conclusion, the IL-CNC@DP in comparison to the DP confirmed exceptional results proving that the modification enhanced the remediation of the Li⁺ from water. Furthermore, the selectivity of IL-CNC@DP towards real groundwater samples isolated in Qatar depends upon the physicochemical characteristics of each element.

Preparation of binder-less activated char briquettes from pyrolysis of sewage sludge for liquid-phase adsorption of methylene blue

Binder-less activated char briquettes from sewage sludge were prepared and used for the liquid-phase adsorption of methylene blue. The properties of sludge char briquettes prepared under the different initial sludge moisture content, compression pressure, and heating rate were systematically investigated through the tests of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), surface and mechanical properties, burn-off rates, methylene blue adsorption kinetics and isotherms. All of the prepared briquettes presented hierarchical structures and microporous/mesoporous characteristics, and the increase of initial sludge moisture content from 10 to 30 wt% resulted in a great increase of surface area (S_BET), total pore volume (V_T), apparent density, and a slight decrease of mechanical performance. The decrease of compression pressure markedly enhanced the equilibrium adsorption capacity (q_{e, exp}), owing to the decreased diffusion resistance and blockage of diffusion pathways inside briquettes. In consideration of the mechanical performance and adsorption capacity, the optimum preparation condition was obtained at the initial moisture content of 30 wt%, compression pressure of 25 MPa, and heating rate of 10 °C/min, in which the axial compressive strength (ACS) and q_{e, exp} of the prepared briquettes were as high as 22.2 ± 3.1 kg/m² and 316.9 mg/g. The results also showed that the equilibrium adsorption data fit well into the pseudo-first order model system, and the adsorption isotherms followed the Langmuir isotherm model, suggesting that the adsorption process was attributed to physical adsorption, and was inclined to happen on the adsorption sites with the same energy level. Finally, the thermal regeneration tests demonstrated that the binder-less briquette had a good regeneration performance and was worthy of reusing for industrial applications.

Hierarchically 3-D Porous Structure of Silk Fibroin-Based Biocomposite Adsorbent for Water Pollutant Removal

This study explored the tunability of a 3-D porous network in a freeze-dried silk fibroin/soursop seed (SF:SS) polymer composite bioadsorbent. Morphological, physical, electronic, and thermal properties were assessed using scanning electron microscopy, the BET N2 adsorption-desorption test, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). A control mechanism of pore opening–closing by tuning the SS fraction in SF:SS composite was found. The porous formation is apparently due to the amount of phytic acid as a natural cross-linker in SS. The result reveals that a large pore radius is formed using only 20% wt of SS in the composite, i.e., SF:SS (4:1), and the fibrous network closes the pore when the SS fraction increases up to 50%, i.e., SF:SS (1:1). The SF:SS (4:1) with the best physical and thermal properties shows an average pore diameter of 39.19 nm, specific surface area of 19.47 m2·g−1, and thermal stability up to ~450 °C. The removal of the organic molecule and the heavy metal was assessed using crystal violet (CV) dye and the Cu2+ adsorption test, respectively. The adsorption isotherm of both CV and Cu2+ on SF:SS (4:1) follows the Freundlich model, and the adsorption kinetic of CV follows the pseudo-first-order model. The adsorption test indicates that physisorption dominates the adsorption of either CV or Cu2+ on the SF:SS composites.

Glycidyl and Methyl Methacrylate UV-Grafted PDMS Membrane Modification toward Tramadol Membrane Selectivity

Pharmaceutical wastewater pollution has reached an alarming stage, as many studies have reported. Membrane separation has shown great performance in wastewater treatment, but there are some drawbacks and undesired byproducts of this process. Selective membranes could be used for pollutant investigation sensors or even for pollutant recovery. The polydimethylsiloxane (PDMS) membrane was first tested on separated and mixed antibiotic (ATB) water solutions containing sulfamethoxazole (SM), trimethoprim (TMP), and tetracycline (TET). Then, the bare and ultra-violet grafted (UV-grafted) PDMS membranes (MMA-DMAEMA 10, GMA-DMAEMA 5, and GMA-DMAEMA 10) were tested in tramadol (TRA) separation, where the diffusion coefficient was evaluated. Finally, the membranes were tested in pertraction with a mixture of SM, TMP, TET, and TRA. The membranes were characterized using the following methods: contact angle measurement, FTIR, SEM/EDX, and surface and pore analysis. The main findings were that TET was co-eluted during mixed ATB pertraction, and GMA-DMAEMA 5 was found to selectively permeate TRA over the present ATBs.

Removal of phenol from aqueous solution by coupling alternating current with biosorption

The present research was devoted to water decontamination through the valorization of cellulosic fibers for the preparation of performing biosorbent, with high pollutant-uptake capacity and low cost. Luffa cylindrica (L.C) and zinc oxide were chosen for the synthesis of hybrid materials by precipitation with and without alternating current (AC). AC was used as a new alternative able to accelerate the reaction kinetics and to enhance the biosorption speed. The potential to remove phenol, from aqueous solution by coupling biosorption and AC, was highlighted. Pure L.C and hybrid materials (L.C + 4% Zn²⁺) synthesized with and without AC were chosen for the biosorption tests. The effects of pH, initial concentration, frequency, and contact time were studied. The efficiency of the coupling process was evaluated according to the quality of the treated water before and after purification. Results have shown that the percentages of chemical oxygen demand (COD), total organic carbon (TOC), germination indexes, and phenol removals have increased when adopting the coupling process. The maximal uptakes of phenol reached 15.4, 28.07, and 28.9 mg g^-1 for a concentration of 30 mg L^-1 of phenol, respectively, for raw L.C, L.C + 4% Zn²⁺ + AC, and L.C + 4% Zn²⁺ at pH = 2. Quantitative and qualitative characterizations confirmed the efficiency of the synthesized hybrid materials compared with pure L.C. The fractal model of Brouers Sotolongo was chosen for the description of the random distribution of the active sites. The kinetic and isotherm data showed a good correlation with the experimental results.

Valorization of Agri-Food Wastes as Sustainable Eco-Materials for Wastewater Treatment: Current State and New Perspectives

The paper addresses environmental protection by valorizing an important agri-food waste category, namely fruit and vegetables with focusing on the main characteristics regarding consumption, waste quantities, and ways for valorizing these materials. Thus, vast research was undertaken in order to emphasize the main commodities and their potential application as adsorbents for organic and inorganic pollutants. The main methods or treatment techniques applied for the valorization of eco-materials as adsorbents were presented and the principal efficiency results were indicated. The advantages and disadvantages of using these eco-materials as adsorbents in wastewater treatment were revealed and future recommendations were established. According to the international statistics, the most purchased and consumed five commodities were studied regarding waste generations as potential conversion into eco-materials with an adsorbent role for water pollutants. Thus, the performances for adsorbents based on fruit wastes (such as citrus, banana, apples, grapes, mango) and vegetable wastes (such as potatoes, tomatoes, cabbage, carrots, cauliflower, and/or broccoli) were studied and highlighted in this research.

Biosorbents from Plant Fibers of Hemp and Flax for Metal Removal: Comparison of Their Biosorption Properties

Lignocellulosic fibers extracted from plants are considered an interesting raw material for environmentally friendly products with multiple applications. This work investigated the feasibility of using hemp- and flax-based materials in the form of felts as biosorbents for the removal of metals present in aqueous solutions. Biosorption of Al, Cd, Co, Cu, Mn, Ni and Zn from a single solution by the two lignocellulosic-based felts was examined using a batch mode. The parameters studied were initial metal concentration, adsorbent dosage, contact time, and pH. In controlled conditions, the results showed that: (i) the flax-based felt had higher biosorption capacities with respect to the metals studied than the hemp-based felt; (ii) the highest removal efficiency was always obtained for Cu ions, and the following order of Cu > Cd > Zn > Ni > Co > Al > Mn was found for both examined biosorbents; (iii) the process was rapid and 10 min were sufficient to attain the equilibrium; (iv) the efficiency improved with the increase of the adsorbent dosage; and (v) the biosorption capacities were independent of pH between 4 and 6. Based on the obtained results, it can be considered that plant-based felts are new, efficient materials for metal removal.

Aloe vera as Promising Material for Water Treatment: A Review

Aloe vera plant offers a sustainable solution for the removal of various pollutants from water. Due to its chemical composition, Aloe vera has been explored as coagulant/flocculant and biosorbent for water treatment. Most of the used materials displayed significant pollutants removals depending on the used preparation methods. AV-based materials have been investigated and successfully used as coagulant/flocculant for water treatment at laboratory scale. Selected AV-based materials could reduce the solids (total suspended solids (TSS), suspended solids (SS), total dissolved solids (TDS), and dissolved solids (DS)), turbidity, chemical oxygen demand (COD), biochemical oxygen demand (BOD), heavy metals, and color, with removal percentages varied depending on the coagulant/flocculant materials and on the wastewater characteristics. In the same context, AV materials can be used as biological flocculant for wastewater sludge treatment, allowing good solid–liquid separation and promoting sludge settling. Moreover, using different methods, AV material-based biosorbents were prepared and successfully used for pollutants (heavy metal dyes and phenol) elimination from water. Related results showed significant pollutant removal efficiency associated with an interesting adsorption capacity comparable to other biosorbents derived from natural products. Interestingly, the enzymatic system of Aloe vera (carboxypeptidase, glutathione peroxidase, and superoxide dismutase) has been exploited to degrade textile dyes. The obtained results showed high promise for removal efficiencies of various kinds of pollutants. However, results varied depending on the methodology used to prepare the Aloe vera based materials. Because of its valuable properties (composition, abundance, ecofriendly and biodegradable), Aloe vera may be useful for water treatment.

Hydrogel Based on Tricarboxi-Cellulose and Poly(Vinyl Alcohol) Used as Biosorbent for Cobalt Ions Retention

A biomaterial based on poly(vinyl alcohol) reticulated with tricarboxi-cellulose obtained by TEMPO oxidation (OxC25) was used as a new biosorbent for Co(II) ions retention from aqueous solutions. The biosorption process of Co(II) ions was studied while mainly considering the operational factors that can influence it (i.e., biosorbent concentration, pH of the aqueous media, temperature and contact time of the phases). The maximum adsorption capacity was 181.82 mg/g, with the biosorption well fitted by the Langmuir model. The kinetic modeling of the biosorption process was based on certain models: Lagergreen (pseudo first order model), Ho (pseudo second order model), Elovich (heterogeneous biosorbent model), Webber-Morris (intraparticle diffusion model) and McKay (film diffusion model). The corresponding kinetic model suggests that this biosorption process followed a pseudo-second order kinetic model and was developed in two controlled steps beginning with film diffusion and followed by intraparticles diffusion.

Husk of Agarwood Fruit-Based Hydrogel Beads for Adsorption of Cationic and Anionic Dyes in Aqueous Solutions

Hydrogel beads based on the husk of agarwood fruit (HAF)/sodium alginate (SA), and based on the HAF/chitosan (CS) were developed for the removal of the dyes, crystal violet (CV) and reactive blue 4 (RB4), in aqueous solutions, respectively. The effects of the initial pH (2–10) of the dye solution, the adsorbent dosage (0.5–3.5 g/L), and contact time (0–540 min) were investigated in a batch system. The dynamic adsorption behavior of CV and RB4 can be represented well by the pseudo-second-order model and pseudo-first-order model, respectively. In addition, the adsorption isotherm data can be explained by the Langmuir isotherm model. Both hydrogel beads have acceptable adsorption selectivity and reusability for the study of selective adsorption and regeneration. Based on the effectiveness, selectivity, and reusability of these hydrogel beads, they can be treated as potential adsorbents for the removal of dyes in aqueous solutions.

Adsorptive removal of direct red 80 and methylene blue from aqueous solution by potato peels: a comparison of anionic and cationic dyes

Adsorption of direct red 80 (DR 80) and methylene blue (MB) from aqueous solutions on potato peels (PP) has been compared. The use of peels in decontamination technology is very promising given the near zero-cost for the synthesis of those adsorbents. The selected potato peels were first analyzed by scanning using electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR). Then the adsorption behavior was studied in a batch system. The adsorption process is affected by various parameters such as the solution pH (2-11), the initial concentration of the dye (20, 50, 100, 150 and 200 mg L^-1), the adsorbent dose (0.1-3%), the temperature (303.16 K, 313.16 K, and 323.16 K), agitation (up to 250 rpm), as well as the contact time. Adsorption isotherms of the studied dye on the adsorbent were determined and compared with the Langmiur, Freundlich and Temkin adsorption models. The results show that the data was most similar to the Freundlich isotherm (R² = 0.99). The maximum adsorption capacities (Q_max) of MB and DR 80 by the PP at temperatures 303.16 K, 313.16 K and 323.16 K were found to be approximately 97.08 mg g^-1; 45.87 mg g^-1; 61.35 mg g^-1 and 27.778 mg g^-1; 45.45 mg g^-1; and 32.258 mg g^-1. The kinetic data was compared to the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. This revealed that adsorption of methylene blue onto PP abided mostly to the pseudo-second-order kinetic model. Calculations of various thermodynamic parameters such as enthalpy change (ΔH), entropy change (ΔS), and free energy change (ΔG) display the endothermic and spontaneous nature of the adsorption process.

A physicochemical model for rationalizing SARS-CoV-2 concentration in sewage. Case study: The city of Thessaloniki in Greece

Detection of SARS-CoV-2 in sewage has been employed by several researchers as an alternative early warning indicator of virus spreading in communities, covering both symptomatic and asymptomatic cases. A factor that can seriously mislead the quantitative measurement of viral copies in sewage is the adsorption of virus fragments onto the highly porous solids suspended in wastewater, making them inaccessible. This depends not only on the available amount of suspended solids, but also on the amount of other dissolved chemicals which may influence the capacity of adsorption. On this account, the present work develops a mathematical framework, at various degrees of spatial complexity, of a physicochemical model that rationalizes the quantitative measurements of total virus fragments in sewage as regards the adsorption of virus onto suspended solids and the effect of dissolved chemicals on it. The city of Thessaloniki in Greece is employed as a convenient case study to determine the values of model variables. The present data indicate the ratio of the specific absorption (UV254/DOC) over the dissolved oxygen (DO) as the parameter with the highest correlation with viral copies. This implies a strong effect on viral inaccessibility in sewage caused (i) by the presence of humic-like substances and (ii) by virus decay due to oxidation and metabolic activity of bacteria. The present results suggest days where many fold corrections in the measurement of viral copies should be applied. As a result, although the detected RNA load in June 2020 is similar to that in April 2020, virus shedding in the city is about 5 times lower in June than in April, in line with the very low SARS-CoV-2 incidence and hospital admissions for COVID-19 in Thessaloniki in June.

Waste Cleaning Waste: Combining Alginate with Biowaste-Derived Substances in Hydrogels and Films for Water Cleanup

Biowaste-derived substances isolated from green compost (BBS-GC) are environmentally friendly reactants similar to humic substances, which contain multiple functionalities, that are suitable for adsorbing different kinds of pollutants in wastewater. Herein, sodium alginate (derived from brown algae) cross-linked with both Ca2+ ions and BBS-GC in the form of hydrogels and dried films are proposed as green, easy-to-form, and handleable materials for tertiary water treatments. The results show that both hydrogels and films are mechanically stable and can effectively remove differently charged dyes through an adsorption mechanism that can be described by the Freundlich model. BBS-GC-containing gels always performed better than samples prepared without BBS-GC, revealing that such unconventional materials can integrate waste valorization and water decontamination, potentially providing social and environmental benefits.

Sorption, mechanism, and behavior of sulfate on various adsorbents: A critical review

Sulfate decontamination has drawn widespread attention due to its harmful effects by broad human and animal exposure in recent decades. Adsorption is one of the most promising methods for sulfate decontamination. This review categorized various sulfate adsorbents, discussed the adsorption behavior, and introduced effective adsorbents in detail in terms of their preparation, characterization, and affecting factors on adsorption efficiency. Moreover, adsorption mechanisms of sulfate on different adsorbents are reviewed based on the intermolecular interaction, equilibrium, thermodynamic, and kinetic studies. Among natural bioadsorbents, synthesized-organic, and synthesized-inorganic adsorbents chitin-based shrimp shells (156 mg/g), bagasse pith cellulose-based (526.32 mg/g), and ZrO(OH)₂/Y-Zeolite (284.22 mg/g) showed the significant capacity for sulfate uptake from aqueous solution, respectively. Although natural adsorbents have been proved to be inexpensive and efficient, they are not as popular as synthesized adsorbents for sulfate decontamination in recent years due to their low recoverability and reusability. The adsorption mechanism of sulfate to various adsorbents is generally attributed to electrostatic interactions, covalent or ionic bonding, and hydrogen bonding. Based on equilibrium studies, sulfate adsorption processes were done mainly homogeneously for most of the adsorbents; however, there are some exceptions of the heterogeneous adsorption process of sulfate, which is done mostly for adsorbents that remove sulfate through hydrogen and covalent bonding. The kinetic studies illustrated that both film diffusion and pore-diffusion could control sulfate uptake by the various adsorbents. The thermodynamic studies showed that the sulfate adsorption is endothermic and spontaneous except for the sulfate removal by polypyrrole-modified activated-carbons and LDH-HPI mine waste, which requires energy for adsorption.

Modified wheat straw-derived graphene for the removal of Eriochrome Black T: characterization, isotherm, and kinetic studies

A cost-effective and environment-benign adsorbent was prepared from an abundant agro-waste material. Wheat straw was reduced to graphene and then modified by crosslinking to epichlorohydrin. During the conversion process of wheat straw to graphene, the specific surface area increased more than 100 times (from 4 to 415 m² g^-1). The adsorption efficiency of raw wheat straw, graphene nanosheets, and modified graphene against Eriochrome Black T (EBT) were 8.0, 34.7, and 74.4%, respectively. The modified graphene was further investigated for the effect of environmental condition, i.e., pH (3 to 11), EBT concentration (25-100 mg L^-1), adsorbent dosage (0.25-0.75 g L^-1), contact time (5-60 min), and solution temperature (30-60 °C). The dye removal remained at a high level under a wide range of pH from 3 to 9. The EBT removal decreased from 87.3 to 54.5 by increasing dye concentration and increased from 38.2 to 85.4% by increasing adsorbent dose in the studied ranges. Dye removal also increased by mixing time from 5 to 30 min, whereas a slight drop was observed by continuing agitation up to 60 min. Conducting experiments at various temperatures revealed an endothermic process. Pseudo-first-order and pseudo-second-order models were adequate to represent the adsorption kinetics. Isotherm models suggest a multilayer adsorption of EBT molecules on heterogeneous modified graphene surface with a maximum adsorption capacity of 146.2 mg g^-1. The present work demonstrated that the modified graphene obtained from available and low-cost agro-wastes could be used effectively as adsorbent against EBT from aqueous media.

Predicted structure and selectivity of 3d transition metal complexes with glutamic N,N-bis(carboxymethyl) acid

Structure and selectivity of 3d transition metal complexes with glutamic N,N-bis(carboxymethyl) acid are analyzed and predicted from DFT calculations.

Kinetics and Thermodynamics Studies for Cadmium (II) Adsorption onto Functionalized Chitosan with Hexa-Decyl-Trimethyl-Ammonium Chloride

A new adsorbent material was obtained by functionalization of chitosan with hexa-decyl-trimethyl-ammonium chloride and tested as an adsorbent for Cd(II) ions. Functionalization is due to the desire to improve the adsorbent properties of the biopolymer used for removal of metallic ions. Obtained material was characterized by FTIR (Fourier Transform InfraRed spectroscopy), SEM (Scanning Electron Microscopy) and EDX (Energy dispersive X-ray Spectroscopy). To prove the Cd(II) adsorption mechanism, we performed adsorption tests determining influence of biopolymer ratio, pH, contact time, temperature and Cd(II) initial concentration. Obtained experimental data were modeled using two kinetics models: pseudo-first-order and pseudo-second-order models. Cd(II) adsorption kinetics was better described by pseudo-second-order model. Further, experimental data were fitted using three different adsorption isotherms: Langmuir, Freundlich and Sips. The studied adsorption process is well described by the Sips adsorption isotherm, when the maximum adsorption capacity value is near the experimental one. Likewise, we evaluated the values of thermodynamic parameters which indicate that the studied process is an endothermic and spontaneous one, being a physical adsorption. Prepared adsorbent materials have a maximum adsorption capacity of 204.3 mg Cd²⁺ per gram at pH > 4.0 and 298 K. In addition, this material was reused for Cd²⁺ recovery for 20 times.

Adsorption of methylene blue on sodium alginate-flax seed ash beads: Isotherm, kinetic and thermodynamic studies

In the present study, the adsorptive removal of methylene blue (MB) from wastewater was studied using the novel composite prepared by sodium alginate (SA) and flax seed ash (FS). The adsorption of MB was carried out using the composite beads consisting of different weight amounts of FS at different pH values and temperatures using different dye concentrations. The characterization studies of the composite beads were performed using Fourier-Transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and Brunauer-Emmett-Teller and Barrett-Joyner-Hallenda (BET-BJH) analyses. BET and BJH surface area values of SA-FS adsorbent beads were found to be 45.01 m²/g and 14.35 m²/g, respectively. During the studies, it was determined that the adsorption percentage of MB reached the maximum with 90% at pH = 7 and 50 °C. Furthermore, Langmuir model fits well for the adsorption of MB using SA-FS with different FS ratios, SA, and FS adsorbents. The maximum adsorption capacity obtained from Langmuir model was found to be 333.3 mg/g for SA-FS-2 composite beads at pH = 7 and 50 °C. The adsorption kinetics were interpreted well by pseudo-second order model for SA, FS and SA-FS adsorbents. The calculated thermodynamic parameters indicated that MB adsorption by FS, SA, and SA-FS were spontaneous and an endothermic.

The Equilibrium, Kinetics, and Thermodynamics Studies of the Sorption of Methylene Blue from Aqueous Solution Using Pulverized Raw Macadamia Nut Shells

In this study, the potential for pulverized raw macadamia nut shell (MNS) for the sequestration of methylene blue from aqueous media was assessed. The sorbent was characterized using scanning electron microscopy for surface morphology, functional group analysis was performed with a Fourier-transform infrared spectrometer (FT-IR), and Brunauer-Emmett-Teller (BET) isotherm was used for surface area elucidation. The effects of contact time, sorbent dosage, particle size, pH, and change in a solution matrix were studied. Equilibrium data were fitted using Temkin, Langmuir, and Freundlich adsorption isotherm models. The sorption kinetics was studied using the Lagergren pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The feasibility of the study was established from the thermodynamic studies. A surface area of 2.763 m²/g was obtained. The equilibrium and kinetics of sorption was best described by the Langmuir and the pseudo-second-order models, respectively. The sorption process was spontaneous (-ΔG ⁰=28.72 - 31.77 kJ/mol) and endothermic in nature (ΔH ⁰=17.45 kJ/mol). The positive value of ΔS⁰ (0.15 kJ/molK) implies increased randomness of the sorbate molecules at the surface of the sorbent. This study presents sustainable management of wastewater using MNS as a potential low-cost sorbent for dye decontamination from aqueous solution.

Multivariate analysis for FTIR in understanding treatment of used cooking oil using activated carbon prepared from olive stone

In this study, activated carbons prepared from the green and black olive stone (green OSAC and black OSAC) were used as adsorbents to investigate their removal efficiencies for oxidation products and polar compounds from used sunflower and corn cooking oils. The degree of oxidation level and polar compounds were evaluated using Fourier transform infrared (FTIR) with the principal component analysis and ultra-performance liquid chromatography. Two FTIR absorption peaks were used for the oil evaluation, namely 3007-3009 cm-1, which is related to C-H symmetric stretching vibration of the cis double bonds, and ~1743 cm-1, which is related to = CH and ester carbonyl stretching vibration of the functional groups of the triglycerides, C = O. The principal component analysis results showed significant variations in the oxidation level of the sunflower and the corn oils occurred after consecutive heating and French fries frying for 10 days. The oxidation products that are adsorbed on the surface of the OSAC forms π-complexes with the C = C parts of the OSAC system. It can be concluded that the prepared adsorbents can be promising, efficient, economically effective, and environmentally friendly alternative adsorbents for oil treatment applications.

Adsorption of Dye by Waste Black Tea Powder: Parameters, Kinetic, Equilibrium, and Thermodynamic Studies

Waste black tea powder was used as a potential adsorbent to remove methylene blue (MB) from aqueous solution. Several operating factors in adsorption of MB onto waste black tea powder were investigated, including contact time, initial MB concentration, solution pH, adsorption temperature, and dosage of waste black tea powder. Experimental results revealed that the adsorption efficiency increased with contact time and solution pH values and decreased with initial MB concentration and adsorption temperature. The equilibrium time was estimated to be around 60 min. The maximum adsorption capacity and the highest adsorption efficiency were 302.63 mg·g−1 and 100%, respectively. In kinetic study, pseudo-first-order and pseudo-second-order kinetic models, intraparticle diffusion model, and Boyd and Elovich models were employed to analyze the adsorption behavior and the adsorption mechanism. It was found that the pseudo-second-order kinetic model was suitable to describe the adsorption process, and the calculated equilibrium adsorption capacity was well close to the experimental data for different initial MB concentrations. The internal diffusion was not the only rate-controlling step, and the existence of boundary effect was observed in this study. From isotherm analysis, the equilibrium data were well represented by the Langmuir model, rather than Freundlich, Dubinin–Redushckevich, or Temkin models. The nonlinear fitting for various isotherm models implied that the adsorption behavior between MB and waste black tea powder was complication. Thermodynamic parameters including changes in Gibb’s free energy, enthalpy, and entropy suggested that adsorption of MB onto waste black tea powder was a spontaneous and exothermic process. The multiple regeneration/adsorption experiments indicated that the used black tea powder efficiently remained more than 75% after five cycles using NaOH as a regenerative reagent and thus be used for many times. Therefore, as a low-cost and easily available material, waste black tea powder could be applied in wastewater treatment.