Effects of ionic strength on removal of toxic pollutants from aqueous media with multifarious adsorbents: A review

Defective UiO-66/cellulose nanocomposite aerogel for the adsorption of heterocyclic aromatic amines

Heterocyclic aromatic amines (HAAs), arising as chemical derivatives during the high-temperature culinary treatment of proteinaceous comestibles, exhibit notable carcinogenic potential. In this paper, a composite aerogel (AGD-UiO-66) with high-capacity and fast adsorption of HAAs was made with anchoring defective UiO-66 (D-UiO-66) mediated by lauric acid on the backbone of cellulose nanofibers (CNF). AGD-UiO-66 with hierarchical porosity reduced the mass transfer efficiency for the adsorption of HAAs and achieved high adsorption amount (0.84-1.05 μmol/g) and fast adsorption (15 min). The isothermal adsorption model demonstrated that AGD-UiO-66 belonged to a multilayer adsorption mechanism for HAAs. Furthermore, AGD-UiO-66 was successfully used to adsorb 12 HAAs in different food (roasted beef, roasted pork, roasted salmon and marinade) with high recoveries of 94.65%-104.43%. The intrinsic potential of AGD-UiO-66 demonstrated that it could be widely applicable to the adsorption of HAAs in foods.

Effects of Ionic Interferents on Electrocatalytic Nitrate Reduction: Mechanistic Insight

Nitrate, a prevalent water pollutant, poses substantial public health concerns and environmental risks. Electrochemical reduction of nitrate (eNO3RR) has emerged as an effective alternative to conventional biological treatments. While extensive lab work has focused on designing efficient electrocatalysts, implementation of eNO3RR in practical wastewater settings requires careful consideration of the effects of various constituents in real wastewater. In this critical review, we examine the interference of ionic species commonly encountered in electrocatalytic systems and universally present in wastewater, such as halogen ions, alkali metal cations, and other divalent/trivalent ions (Ca2+, Mg2+, HCO3-/CO32-, SO42-, and PO43-). Notably, we categorize and discuss the interfering mechanisms into four groups: (1) loss of active catalytic sites caused by competitive adsorption and precipitation, (2) electrostatic interactions in the electric double layer (EDL), including ion pairs and the shielding effect, (3) effects on the selectivity of N intermediates and final products (N2 or NH3), and (4) complications by the hydrogen evolution reaction (HER) and localized pH on the cathode surface. Finally, we summarize the competition among different mechanisms and propose future directions for a deeper mechanistic understanding of ionic impacts on eNO3RR.

Microplastic-mediated environmental behavior of metal contaminants: mechanism and implication

Microplastics (MPs) and metals are currently two of the most concerning environmental pollutants due to their persistent nature and potential threats to ecosystems and human health. This review examines the intricate interactions between MPs and metals in diverse environmental compartments, including aquatic, terrestrial, and atmospheric environments by focusing on the complex processes of adsorption and desorption and the mechanisms that govern these interactions. MPs act as carriers and concentrators of metals in aquatic and terrestrial environments, affecting the bioavailability and toxicity of these contaminants to aquatic and terrestrial organisms. This review highlights the existing challenges and constraints associated with current analytical methods, including microscopy, spectroscopy, and isotherm models in studying microplastic-heavy metal interactions. Moreover, we identified the knowledge gaps and future research directions that can enhance our understanding of the dynamic interplay between MPs and metals in various environmental settings.

Magnetized cubic zinc MOFs for efficient removal of hazardous cationic and anionic dyes in aqueous solutions

A significant amount of dye runoff and aqueous waste are released from the manufacturing process of dyes with intense and permanent colors, which are undesirable from a cultural and ecological aspect. In this paper, we present a green, simple, low-effort, and energy-efficient method of creating magnetized cubic Zn-MOFs for the adsorption and elimination of various organic dyes. Magnetic iron oxide materials with a hierarchical structure were loaded and doped into cubic zinc metal-organic frameworks (MDLZ). High magnetic characteristics, chemical stability, minimal toxicity, and ease of removing various dyes from aqueous effluents are all exhibited by the developed MDLZ adsorbent. To assess MDLZ's capacity to adsorb organic dyes from an aqueous solution, organic dyes such as Crystal Violet (CV), Neutral Red (NR), and Congo Red (CR) were used as model materials. Many adsorption factors were examined, including temperature, pH, contact time, initial concentration, and adsorbent dosage. Under optimal elimination circumstances, MDLZ was utilized to evaluate the kinetic, thermodynamic, and isotherm models for the adsorption of CR, NR, and CV dyes. The adsorption capacity (q m) of the MDLZ adsorbent at 25 °C was 39.37 mg g-1 for CV, 239.81 mg g-1 for CR, and 321.54 mg g-1 for NR, which is significantly higher than those of other adsorbents reported. The magnetized nanocubes' large surface area and uniform micropores enabled them to eliminate a large number of organic dyes from wastewater effectively, and their strong adsorption capability persisted even after four reuse cycles. The microporous MLDZ adsorbent offers a simple and effective method for handling industrial effluents and filtration of water.

Opportunity for a greener recovery of dysprosium(III) from secondary sources by a novel Mannich reaction-modified phosphorylated chitosan hydrogel

The depleting supply of natural sources of rare earth elements (REE) is a concern to many nations as demand for advanced technology is becoming vital for national security. In this communication, the recovery of dysprosium(III) from aqueous systems was exemplified by a modified phosphorylated chitosan (PCs/MB) prepared by the C-Mannich reaction of phosphorylated chitosan, glutaraldehyde, and 4-hydroxycoumarin in ethanolic solution. Batch adsorption studies achieved a maximum adsorption capacity (qmax) of 34 mg/g at 25 °C and pH = 5.4 for 2 h. Fourier Transform-Infrared Spectroscopy, elemental mapping, and quantitative analyses revealed ion-exchange mechanism with C6-phosphate and a synergistic complexation with the amino group between two hexose units of the chitosan chain confirming the correlation provided by the pseudo-second order kinetics (R2 = 0.9996), extrapolated mean free energy of adsorption (Eads) of 12.9 kJ/mol from the corrected Dubinin-Radushkevich isotherm, and the extrapolated enthalpy of adsorption (ΔH0ads) of -42.4 kJ/mol from the linearized Van't Hoff plot. Competitive adsorption with iron(II), cerium(III), and neodymium(III) demonstrated preferential removal of dysprosium(III) and complete exclusion of iron(II), which illustrates potential application in the separation of REE from electronic wastes.

Innovative recovery of matrix layered double hydroxide from simulated acid mine wastewater for the removal of copper and cadmium from wastewater

This study innovatively added biochar to optimize regulation in the neutralization process of simulated acid mine drainage (AMD) and recovered a new type of matrix layered double hydroxides (MLDH), which can be used to remove copper (Cu(II)) and cadmium (Cd(II)) from wastewater. A series of batch experiments show that MLDH with strong selective removal ability of Cu(II) and Cd(II) can be successfully obtained by adding biochar (BC) at pH = 5 end in the neutralization process. Kinetic and isotherm modeling studies indicated that the removal of Cu(II) and Cd(II) by the MLDH was a chemical multilayer adsorption process. The removal mechanism of Cu(II) and Cd(II) was further analyzed through related characterization analysis with contribution rate calculation: the removal rates of Cu(II) and Cd(II) by ion exchange were 42.7% and 26%, while that by precipitation were 34.5% and 49.9%, respectively. This study can provide a theoretical reference and experimental basis for the recovery and utilization of valuable by-products in AMD and the treatment of heavy metal wastewater.

Utilization of biochar for remediation of heavy metals in aqueous environments: A review and bibliometric analysis

Biochar usage for removing heavy metals from aqueous environments has emerged as a promising research area with significant environmental and economic benefits. Using the PICO approach, the research question aimed to explore using biochar to remove heavy metals from aqueous media. We merged the data from Scopus and the Web of Science Core Collection databases to acquire a comprehensive perspective of the subject. The PRISMA guidelines were applied to establish the search parameters, identify the appropriate articles, and collect the bibliographic information from the publications between 2010 and 2022. The bibliometric analysis showed that biochar-based heavy metal remediation is a research field with increasing scholarly attention. The removal of Cr(VI), Pb(II), Cd(II), and Cu(II) was the most studied among the heavy metals. We identified five main clusters centered on adsorption, water treatment, adsorption models, analytical techniques, and hydrothermal carbonization by performing keyword co-occurrence analysis. Trending topics include biochar reusability, modification, acid mine drainage (AMD), wastewater treatment, and hydrochar. The reutilization of heavy metal-loaded spent biochar includes transforming it into electrodes for supercapacitors or stable catalyst materials. This study provides a comprehensive overview of biochar-based heavy metal remediation in aquatic environments and highlights knowledge gaps and future research directions.

Treatment of high-strength saline bilge wastewater by four pilot-scale aerobic moving bed biofilm reactors and comparison of the microbial communities

Four Pilot-scale Moving Bed Biofilm Reactors (MBBRs) were operated for the treatment of real, saline, bilge wastewater. The MBBRs were connected in pairs to create two system configurations with different filling ratios (20%, 40%) and were operated in parallel. The inflow organic loading rate (OLR) varied from 3.6 ± 0.2 to 7.8 ± 0.6 g COD L-1 d-1, salinity was >15 ppt and three hydraulic residence times (HRTs) were tested 48, 30 and 24 h. In both systems, the first-stage bioreactors (R1 and R3) eliminated the higher part of the organic load (57%-65%). The second-stage bioreactors (R2 and R4) removed an additional fraction (18%-31%) of the organic load received by the effluent of R1 and R3, respectively. The microbial communities of the influent wastewater, suspended, and attached biomass were determined using 16S rRNA gene amplicon sequencing analysis. The evolution of the microbial communities was investigated and compared over the different operational phases. The microbial communities of the biofilm presented higher diversity and greater stability in composition over time, while the suspended biomass exhibited intense and rapid changes in the dominance of genera. Proteobacteria, Bacteroidetes and Firmicutes were highly present in the biofilm. The genera Celeribacter, Novispirillum, Roseovarius (class: Alphaproteobacteria) and Formosa (class: Flavobacteriia) were highly present during all operational phases. Principal Component Analysis (PCA) was used to identify similarities between samples, exhibiting high relation of samples according to the series of the bioreactor (1st, 2nd).

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite-Water Interface by Adsorption of Rb+ and Halides (Cl- , Br- , I- ) at High Salinity

Classical electric double layer (EDL) models have been widely used to describe ion distributions at charged solid-water interfaces in dilute electrolytes. However, the chemistry of EDLs remains poorly constrained at high ionic strength where ion-ion correlations control non-classical behavior such as overcharging, i. e., the accumulation of counter-ions in amounts exceeding the substrate's surface charge. Here, we provide direct experimental observations of correlated cation and anion distributions adsorbed at the muscovite (001)-aqueous electrolyte interface as a function of dissolved RbBr concentration ([RbBr]=0.01-5.8 M) using resonant anomalous X-ray reflectivity. Our results show alternating cation-anion layers in the EDL when [RbBr]≳100 mM, whose spatial extension (i. e., ~20 Å from the surface) far exceeds the dimension of the classical Stern layer. Comparison to RbCl and RbI electrolytes indicates that these behaviors are sensitive to the choice of co-ion. This new in-depth molecular-scale understanding of the EDL structure during transition from classical to non-classical regimes supports the development of realistic EDL models for technologies operating at high salinity such as water purification applications or modern electrochemical storage.

Prediction of metformin adsorption on subsurface sediments based on quantitative experiment and artificial neural network modeling

Metformin (MET), a widely employed hypoglycemic pharmaceutical agent, has been frequently detected within groundwater, which has posed a threat to ecosystems and human health. However, the adsorption behavior of MET onto distinct constituent aquitards and aquifers sediments remains shrouded in uncertainty. To reveal the adsorption capacities and mechanisms of diverse sedimentary matrices, we delved into a series of adsorption experiments involving MET on 37 subsurface sediment samples obtained from four boreholes (ranging from 0 to 30 m in depth) in the Jianghan Plain. The quantitative analysis revealed that a majority of the sedimentary compositions consisted of clay minerals (mainly chlorite, montmorillonite and albite), with MET exhibiting considerable variability in across different sediment components (ranging from 15.5 to 489.4 mg/kg). In general, MET adsorption declined in proportion to an increase in quartz composition and depth. Consequently, an artificial neural network model was constructed (R2 = 0.971) to assess the influence of sediment composition on MET adsorption, and thereby elucidating the dominant roles played by chlorite and montmorillonite in this process. Notably, electrostatic attraction, cation exchange, and chemical bonding emerged as the primary mechanisms governing MET adsorption on sediments, particularly those rich in clay minerals. By shedding light on the adsorption mechanism of MET on clay-dominated subsurface sediments, our findings have contributed to a quantitative understanding of MET's adsorption capacity and have highlighted the associated environmental risks.

Enhanced adsorption of diclofenac onto activated carbon derived from PET plastic by one-step pyrolysis with KOH

Plastic pollution is a severe threat to the health of ecosystems, and recycling plastics is recognized as a key control strategy. This study used the one-step pyrolysis assisted with KOH activation to recycle the widely used polyethylene terephthalate (PET) plastic as activated carbon (PET-AC) which was subsequently applied to adsorb diclofenac (DCF), a frequently detected emerging contaminant in water, for the first time. It was found that both the pyrolysis temperature and the addition of KOH can effectively regulate the pore sizes and volumes of PET-AC. PET-AC obtained at 700 °C demonstrated a high adsorption capacity of DCF up to 179.42 mg g-1 at 45 °C. The adsorption kinetics was conducted with both static jar and dynamic column tests and analyzed with various models. Thermodynamic results demonstrated that the adsorption of DCF was spontaneous and endothermic. The material also presented an excellent potential to adsorb other pharmaceuticals and personal care products in water. XPS and FTIR analysis indicated that the adsorption might be mainly driven by the physical forces, especially π-π interaction and hydrogen bonding. This study provided a reference for recycling waste plastic as an efficient adsorbent to eliminate organic contaminants from water.

Carbonaceous adsorbents in the removal of aquaculture pollutants: A technical review of methods and mechanisms

Carbonaceous adsorbents (CAs) are becoming increasingly popular owing to their low-cost, ease of preparation, and versatility. Meanwhile, aquaculture is becoming a fundamental food industry, globally, due to a wide range of advantages such as economic and nutritional benefits, whilst protecting the depletion of natural resources. However, as with any farming, the technique is known to introduce a plethora of chemicals into the surrounding environment, including antibiotics, nutrients, fertilisers and more. Therefore, the treatment of aquaculture effluent is gaining traction to ensure the sustainable growth of the industry. Although the existing mitigation techniques are somewhat effective, they suffer from degradation of the water quality or harm to local environments/organisms. This article aims to identify the sources and impacts of various aquaculture pollutants. After which the authors will provide an environmentally friendly and novel approach to the treatment of aquaculture effluent using carbonaceous adsorbents. The article will detail discussions about the product life span, including, synthesis, activation, modification, applications in aqueous media, regeneration and End-of-Life (EoL) approaches, with a particular focus on the impacts of competitive adsorption between pollutants and environmental matrices. Some research gaps were also highlighted, such as the lack of literature applying real-world samples, the effects of competitive adsorption and the EoL applications and management for CAs.

Magnetic Polypyrrole-Gelatin-Barium Ferrite Cryogel as an Adsorbent for Chromium (VI) Removal

Polypyrrole-gelatin aerogels, containing magnetic barium ferrite (BaFe) particles, (PPy-G-BaFe) were synthesized by oxidative cryopolymerization and used as adsorbents for the removal of Cr(VI) from aqueous media. The removal was performed at pH 4, which was shown to be the optimal value, due to HCrO4- being the dominant species in these conditions and its more favorable adsorption and reduction compared to CrO42-, present at pH > 4. It was found that the presence of magnetic BaFe particles had no effect on the adsorption performance of PPy aerogels in terms of capacity and kinetics, which was attributed to its relatively low content in the composite. After the adsorption, the presence of chromium in the composites was confirmed by EDX and its electrostatic interaction with the adsorbent was pointed at by vibrational spectroscopy, corresponding to the accepted adsorption mechanism. The adsorption kinetics followed the pseudo-second-order model pointing at chemisorption being the rate-limiting step. The adsorption isotherm data was best fitting with the Temkin model. The maximum adsorption capacity, calculated using the Langmuir model, was 255.8 mg g-1 (the maximum experimental value was 161.6 mg g-1). Additionally, the possibility of Cr(VI) adsorption in the presence of Cl-, Br-, NO3- and SO42- as interfering ions was shown.

Effects of incorporating Mn into goethite on adsorption of dissolved organic matter and potentially toxic elements in soil: Isotherms, kinetics, and mechanisms

Goethite is ubiquitous in the environment and plays key role in preserving dissolved organic matter (DOM) and deactivating potentially toxic elements (PTEs) by adsorbing DOM and PTEs. Various non-Fe metals are usually incorporated into natural goethite, substituting Fe in the goethite structure, which dramatically influence the physico-chemical properties and adsorption behavior of the goethite. In the present study, adsorption of DOM and Pb(II) on Mn-substituted goethite samples was investigated. The results displayed that the specific surface area (SSA) of mineral samples increased by 67.6% as the incorporation of Mn for Fe, from 25.71 m2 g-1 for pure goethite to 43.09 m2 g-1for Mn-goethite. Besides, the Mn substitution caused more hydroxyl groups and relatively fewer positive charges on mineral surface, and Mn in the Mn-goethite samples was predominantly present as Mn(III). The amount of DOM adsorbed to per unit mass of goethite was increased as Mn content increased, which was attributed to Mn incorporation increasing the SSA of mineral samples. However, the SSA-normalized absorption capacity for goethite to DOM was decreased by Mn because Mn substitution decreased the number of positive charges of mineral samples, which weakened the electrostatic attraction between DOM and the minerals. The amount of Pb(II) adsorbed to per unit mass of goethite was increased by Mn substitution, and the amount of Pb(II) adsorbed to per unit SSA of goethite increased as the amount of Mn substitution increased, indicating that the increased capacity for adsorbing Pb was not only caused by the SSA increasing but also by there were more surface hydroxyl groups on the Mn-goethite than pure goethite and Pb(II) preferentially adsorbed to Mn sites on the Mn-goethite. The present study results showed that Mn-goethite could be used to sequester DOM and remediate soil contaminated with PTEs because Mn-goethite has a high adsorption capacity and is environmentally benign.

Extensive sorption of Amoxicillin by highly efficient carbon-based adsorbent from palm kernel: Artificial neural network modeling

In the present study, a new sorbent was fabricated from Palm kernel (PK) by dry thermochemical activation with NaOH and characterized by FTIR, X-ray diffraction, FE-SEM and BET, which was used for the Amoxicillin (AMX) sorption from aqueous solution. The influence of effective parameters such as pH, reaction time, adsorbent dosage, AMX concentration and ionic strength on the sorption efficacy of AMX removal were evaluated. The main functional groups on the surface of the magnetic activated carbon of Palm Kernel (MA-PK) were C-C, C-O, C[bond, double bond]O and hydroxyl groups. The specific surface of char, activated carbon Palm Kernel (AC-PK) and MA-PK were 4.3, 1648.8 and 1852.4 m2/g, respectively. The highest sorption of AMX (400 mg/L) was obtained by using 1 g/L of sorbent at solution pH of 5 after 60 min contact time, which corresponding to 98.77%. Non-linear and linear models of isotherms and kinetics models were studied. The data fitted well with Hill isotherm (R2 = 0.987) and calculated maximum sorption capacity were 719.07 and 512.27 mg/g from Hill and Langmuir, respectively. A study of kinetics shows that the adsorption of AMX follows the Elovich model with R2 = 0.9998. Based on the artificial neural network (ANN) modeling, the MA-PK dosage and contact time showed the most important parameters in the removal of AMX with relative importance of 36.5 and 25.7%, respectively. Lastly, the fabricated MA-PK was successfully used to remove the AMX from hospital wastewater.

Cationic dialdehyde cellulose microfibers for efficient removal of eriochrome black T from aqueous solution

Materials based on cellulose have been widely used as a decontaminant agent of wastewater. However, it can not be found in the literature any application of the cationic dialdehyde cellulose (cDAC) in anionic dye removal. Therefore, this study aims a circular economy concept using sugarcane bagasse to obtain a functionalized cellulose by oxidation and cationization. cDAC was characterized by SEM, FT-IR, oxidation degree, and DSC. Adsorption capacity was evaluated by pH, kinetic, concentration effect, strength ionic tests, and recycling. The kinetic followed Elovich model (R² = 0.92605 for EBT = 100 mg/L) and non-linear Langmuir model (R² = 0.94542), which resulted in a maximum adsorption capacity of 563.30 mg/g. The cellulose adsorbent reached an efficient recyclability of 4 cycles. Thus, this work presents a potential material to become a new, clean, low-cost, recyclable, and environmentally friendly alternative for effluent decontamination-containing dyes.

Valorization of Fibrous Plant-Based Food Waste as Biosorbents for Remediation of Heavy Metals from Wastewater-A Review

Mobilization of heavy metals in the environment has been a matter of concern for several decades due to their toxicity for humans, environments, and other living organisms. In recent years, use of inexpensive and abundantly available biosorbents generated from fibrous plant-based food-waste materials to remove heavy metals has garnered considerable research attention. The aim of this review is to investigate the applicability of using fibrous plant-based food waste, which comprises different components such as pectin, hemicellulose, cellulose, and lignin, to remove heavy metals from wastewater. This contribution confirms that plant-fiber-based food waste has the potential to bind heavy metals from wastewater and aqueous solutions. The binding capacities of these biosorbents vary depending on the source, chemical structure, type of metal, modification technology applied, and process conditions used to improve functionalities. This review concludes with a discussion of arguments and prospects, as well as future research directions, to support valorization of fibrous plant-based food waste as an efficient and promising strategy for water purification.

Comprehensive study on the hydrochar for adsorption of Cd(II): preparation, characterization, and mechanisms

Hydrothermal carbonization process via converting invasive plants into functional materials may provide a novel strategy to comprehensively control and utilized the exotic invasive plants. In this study, Eupatorium adenophorum was utilized to fabricate the hydrochar via hydrothermal carbonization process, which was further applied to remove Cd(II). The results showed that the hydrochar was a mesoporous material with abundant O-containing functional groups (OFPs) on the surface. The adsorption isotherms were fitted by both the Langmuir and Freundlich models, and the maximum adsorption amount achieved 24.53 mg/g. The adsorption dynamics were governed by surface adsorption and film diffusion. pH and ionic strength can exert a strong influence on the adsorption efficiency. The mechanisms on the adsorption of Cd(II) on the hydrochar concluded the pore-filling effects, electrostatic interactions, ion exchange, precipitation, coordination with π electrons, and surface complexation with the OFPs, such as hydroxyl, carboxylic, phenol, acetyl, and ester groups. Thus, hydrothermal carbonization process may provide a promising technique to fabricate the hydrocar for the treatment of Cd(II), which may facilitate comprehensive control of invasive plants and boost to the carbon neutrality.

One-pot synthesis of siliceous ferrihydrite - coated halloysite nanorods in alkaline medium: Structure, properties and cadmium adsorption performance

The application of amorphous ferrihydrite (Fh) for Cd(II) removal is restricted by its unstable and easily transformable nature. Although doping with silicates stabilized ferrihydrite, its product siliceous ferrihydrite (SiFh) again suffered from the disadvantage of spontaneous agglomeration. Herein, ferrihydrite was hybridized with halloysite nanotubes (HNTs) to prepare a novel siliceous ferrihydrite - coated halloysite nanorods (SiFh@HNTs) in alkaline medium, to break through the current barriers. The characterization results showed that SiFh@HNTs could simultaneously overcome the defects of easy phase transformation of ferrihydrite and easy aggregation of SiFh nanoparticles (NPs). Meanwhile, the optimal SiFh@HNT₄₀ with halloysite content of 40 % formed a well-developed mesoporous structure and exhibited the desired surface properties: a high specific surface area of 303.4 m²/g, an isoelectric point as low as pH_iep = 4.5, and rich functional Fe - OH groups. The formation mechanism of such excellent sturcture-properties of SiFh@HNT₄₀ were mainly attributed to two factors: the generation of smaller (∼5 nm) SiFh NPs induced by the integration of halloysite-derived SiO₄^4- into ferrihydrite, and the dispersion of SiFh NPs on clay nanotubes. Furthermore, the adsorption capacity of SiFh@HNT₄₀ for Cd(II) was up to 137.8 mg/g at 30 °C and pH 6, which was much higher than that of aggregated ferrihydrite (11.2 mg/g), halloysite (18.8 mg/g) and goethite (49.4 mg/g). The adsorption thermodynamics study revealed the adsorption of Cd(II) on SiFh@HNT₄₀ was clearly chemisorption with a (ΔH_ads)_q of 43.3 kJ/mol. Characterization results of XPS and FTIR confirmed that the rich Fe - OH groups on SiFh@HNT₄₀ was the main adsorption sites, and Cd(II) was specifically adsorbed by inner-sphere surface complexation. In addition, SiFh@HNT₄₀ had application potential in the mixed-metal wastewaters treatment. Cyclic regeneration experiments showed that SiFh@HNT₄₀ had good regeneration performance and could be reused many times.

Ultra-efficient adsorption of diclofenac sodium on fish-scale biochar functionalized with H3PO4 via synergistic mechanisms

Developing safe and efficient diclofenac sodium (DS) removal technology has become a critical issue. This study synthesized the fish-scale biochar by co-pyrolysis of fish scale and phosphoric acid (H₃PO₄). In addition to increasing the specific surface area and pore volume of fish-scale biochar, H₃PO₄ assisted in the formation of Graphitic N and sp² C, as well as reacting with C═O groups to form a significant number of phosphorus-containing groups. All these functional groups could act as major active sites for DS adsorption. Adsorption data could well fit pseudo-second-order and Langmuir models. The maximum adsorption capacity of FSB_600-15 for DS was 967.1 mg g^-1, which was much better than that reported in the literature. Under the synergistic effect of various mechanisms (pore-filling effect, electrostatic attraction, H-bonding, π-π, and n-π electron donor-acceptor interactions), the DS ultra-efficient adsorption on FSB_600-15 was realized. Meanwhile, the DS adsorption by FSB_600-15 was an endothermic, spontaneous, and entropy-increasing process. Furthermore, the DS adsorption capacity was more than 426.5 mg g^-1 in the actual water, which was sufficient for practical applications.

Versatile crosslinking synthesis of an EDTA-modified UiO-66-NH2/cotton fabric composite for simultaneous capture of heavy metals and dyes and efficient degradation of organophosphate

The metal-organic frameworks/cotton fabric composites (MOFs/CFCs) have emerged as a new type of prospective materials for environmental cleanup, due to their convenient recyclability and high removal efficiency towards hazardous pollutants. However, their practical applications are limited by complicated synthetic conditions, insufficient interface bonding and poor adsorption capacity. Herein, for the first time, a robust ethylenediaminetetraacetic acid (EDTA)-functionalized MOFs/CFC is prepared based on UiO-66-NH₂ crystals by using EDTA dianhydride as the cross-linking agent, and applied for simultaneous removal of heavy metals and dyes, as well as degradation of chemical warfare agents. The as-prepared EDTA-UiO-66-NH₂/CFC shows extraordinary monocomponent adsorption performance with maximum adsorption capacity of 158.7, 126.2, 131.5, 117.4 and 104.5 mg/g for Cd(II), Cu(II), methylene blue, crystal violet and safranin O, respectively. Interestingly, in metal-dyes binary system, the uptake of Cu(II) by EDTA-UiO-66-NH₂/CFC increases significantly when co-existing high concentration of dyes. The results indicate that the synergistic and simultaneous removal of both dyes and metal from complex systems can be realized by EDTA-UiO-66-NH₂/CFC via multiple mechanisms. The EDTA-UiO-66-NH₂/CFC also exhibits an outstanding catalytic performance for degrading dimethyl 4-nitrophenylphosphate. Besides, it can be reused for several times without obvious decrease of its adsorption and catalysis efficiencies. More impressively, the cross-linking reaction approach can not only anchor UiO-66-NH₂ crystals firmly onto cotton fabric, but also facilitate in-situ formation of abundant adsorption sties on the adsorbent surface. Therefore, this work offers a simple and versatile synthetic strategy to develop high-performance environmental material for multiple pollutants remediation.

A stable Fe/Co bimetallic modified biochar for ofloxacin removal from water: adsorption behavior and mechanisms

In this study, Fe-Co-modified biochar (FMBC) loaded with iron (Fe) and cobalt (Co) bimetals after NaOH activation was prepared by pyrolysis using forestry waste cedar bark as a raw material to study its properties and the adsorption of ofloxacin (OFX). The surface structure and chemical properties were analyzed by BET, SEM-EDS, XRD, XPS, and FTIR characterization, and the results showed that the FMBC possessed a larger specific surface area and abundant surface functional groups. FMBC conformed to pseudo-second-order kinetic and Langmuir isotherm models, indicating that the OFX adsorption process on FMBC was a monolayer adsorption process and controlled by chemisorption. The saturation adsorption capacity of FMBC was 10 times higher than that of cedar bark biochar (BC). In addition, the effects of initial pH and coexisting ions on the adsorption process were investigated, and FMBC showed good adsorption, with the best adsorption capacity at pH = 7. Multiple adsorption mechanisms, including physical and chemical interactions, were involved in the adsorption of OFX by FMBC. TG, metal leaching, different water sources, and VSM tests showed that FMBC had good stability and was easily separated from water. Finally, the reusability performance of FMBC was investigated by various methods, and after five cycles it could still reach 75.78-89.31% of the adsorption capacity before recycling. Therefore, the FMBC synthesized in this study is a promising new adsorbent.

Study on the Behaviors and Mechanism of Ni(II) Adsorption at the Hydroxyapatite-Water Interface: Effect of Particle Size

Hydroxyapatite (HAP) was a highly efficient decontamination material for its strong adsorption capacity used in the immobilization of heavy metals, while the particle-size effect was insufficiently investigated during the sorption process. In the present study, the mechanisms of nickel (Ni(II)) adsorption on HAPs with two different particle sizes were investigated by combing batch experiments, desorption, and XRD analysis. The results showed that the adsorption capacity of 20 nm HAP (nano-HAP) was much higher than that of 12 μm HAP (micro-HAP). It was noticed that the results of the present study also clarified the distinct mechanisms in each adsorption process. As for micro-HAP, Ni2+ adsorbed through slow diffusion and replacement with Ca2+ and then incorporated in the lattice at pH between 6.5 and 9.0, which was confirmed by the results of kinetics, thermodynamics, and desorption. And a more compact crystalline structure and irreversible desorption behavior of micro-HAP after Ni(II) adsorption was confirmed by results of XRD and desorption isotherms, respectively. At $\text{pH}>9.0$ , lattice incorporation and precipitation controlled together. However, for nano-HAP, the sharp increase of Ni(II) adsorption and ionic strength dependent at pH 6.5 to 9.0 revealed that the dominant mechanisms were ionic exchange and inner-sphere complexation. XRD results showed that characteristic peaks of cassidyite appeared in Ni(II)-loading nano-HAP. At $\text{pH}>9.0$ , a precipitate of Ni(II) was the dominant mechanism. The experimental finds demonstrated that nanoscale HAP was a more fast, efficient, and desorbable adsorbent than micro-HAP for Ni(II) removal. These findings would be favorable for investigating the removal mechanisms of heavy metals on the HAP materials and designing the synthesis methods.

Zeolite Waste Characterization and Use as Low-Cost, Ecofriendly, and Sustainable Material for Malachite Green and Methylene Blue Dyes Removal: Box–Behnken Design, Kinetics, and Thermodynamics

This study investigated the potential of 4A zeolite, named4AZW in this work, generated by natural gas dehydration units as solid waste after several treatment cycles, as a low-cost adsorbent to separately remove two cationic dyes, methylene blue (MB) and malachite green (MG), from an aqueous solution within a batch process. The adsorbent material was characterized by N2gas adsorption–desorption, X-ray fluorescence spectrometry, X-ray diffraction, FT-IR spectroscopy, and the determination of its cation exchange capacity and point of zero charge. The influence of key operating parameters, such as the pH, adsorbent dosage, ionic strength, contact time, initial dye concentration, and temperature, was investigated. Three independent variables acting on MB adsorption performance were selected from the Box–Behnken design (BBD) and for process modeling and optimization. An analysis of variance (ANOVA), an F-test, and p-values were used to analyze the main and interaction effects. The experimental data were satisfyingly fitted with quadratic regression with adjusted R2= 0.9961. The pseudo-second-order kinetic model described the adsorption of the dyes on 4AZW. The equilibrium data were well-fitted by the Langmuir model for each adsorption system (MB-4AZW and MG-4AZW) with maximum adsorption capacity (qmax) values of 9.95 and 45.64 mg/g, respectively, at 25 °C. Thermodynamics studies showed that both adsorption systems are spontaneous and endothermic.

Investigation of the adsorption behavior of Pb(II) onto natural-aged microplastics as affected by salt ions

In this study, the adsorption behavior of Pb(II) on natural-aged and virgin microplastics in different electrolyte solutions was investigated. The results demonstrated that natural-aged microplastics exhibited higher adsorption capacity for Pb(II) compared to virgin ones, and the addition of CaCl₂ strongly inhibited the adsorption amount of Pb(II). The adsorption kinetics of Pb(II) adsorption were better fitted by the pseudo-second order model and Elovich equation, and were slowed down greatly at higher ionic strength. The rate-limiting steps of adsorption process were dominated by intra-particle diffusion. The adsorption isotherm of Pb(II) onto microplastics affected by salt ions can be well described by Freundlich model, the greater adsorption efficiency of natural-aged microplastics proved that adsorption process was multilayer and heterogeneous. In addition, pH significantly influenced the adsorption of Pb(II) due to the changes electrostatic interactions. The effect of fulvic acid in the electrolyte solutions was also revealed and attributed to the complexation with Na⁺ and Ca²⁺. Furthermore, the higher pH and ionic strength in different environmental water dramatically decreased adsorption capacity onto microplastics. Finally, it's confirmed that the adsorption mechanisms affected by salt ions mainly involve electrostatic interaction, surface complexation, and ionic exchange. These findings indicate that salt ions exert an important influence on the adsorption of heavy metals for MPs, which should be further concerned.

Ammonia removal from industrial effluent using zirconium oxide and graphene-oxide nanocomposites

The present study developed and evaluated nano-adsorbents based on zirconium oxide and graphene oxide (ZrO₂/GO) as a novel adsorbent for the efficient removal of ammonia from industrial effluents. Fourier transform infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscope, Energy-dispersive X-ray Spectroscopy, and X-ray diffraction were used to evaluate and identify the novel adsorbent in terms of morphology, crystallography, and chemical composition. The pH (7), adsorbent quantities (20 mg), adsorbent contact time (30 min) with the sample, and initial ammonia concentration were all tuned for ammonia uptake. To validate ammonia adsorption on the ZrO₂/GO adsorbent, several kinetic models and adsorption isotherms were also utilized. The results showed that the kinetics of ammonia adsorption are of the pseudo-second order due to high R² (>0.99) value as compared first-order (R² = 0.52). The chemical behavior and equilibrium isotherm were analyzed using the isotherm models and Langmuir model provided high R² (>0.98) as compared Freundlich (>0.96). Hence, yielding a maximum uniform equilibrium adsorption capacity of 84.47 mg g^-1. The presence of functional groups on the surface of graphene oxide and ZrO₂ nanoparticles, which interact efficiently with ammonia species and provide an efficient surface for good ammonia removal, is most likely to be responsible.

Mixed matrix of MOF@COF hybrids for enrichment and determination of phenoxy carboxylic acids in water and vegetables

A novel mixed matrix of MOF@COF hybrid was firstly formed by coating of hexahedral cage structure MOF with lightweight porous COF, and applied in dispersive solid-phase extraction of the phenoxy carboxylic acids (PCAs) from water and vegetable samples. Combined with liquid chromatography-tandem mass spectrometry, an excellent method with low limits of detection (0.69-1.79 ng·L^-1/0.002-0.006 ng·g^-1), good reproducibility (1.32%-7.02%/1.81%-6.71%), and excellent linearities (10-1000 ng·L^-1, R ≥ 0.9955/0.04-50 ng·g^-1, R ≥ 0.9966) was established. The adsorption mechanisms deduced that the π-π interaction, hydrophobic effects, hydrogen bond, and halogen bond may promote the excellent adsorption of the PCAs. Finally, the applicability of the method was verified by spiking four kinds of water and vegetable samples with PCAs, and satisfying recoveries were obtained (between 83.3% and 104.9%).

Superhigh co-adsorption of tetracycline and copper by the ultrathin g-C3N4 modified graphene oxide hydrogels

Development of economic and efficient absorbent for the simultaneous removal of antibiotics and heavy metals is needed. In this study, a three-dimensional porous ultrathin g-C₃N₄ (UCN) /graphene oxide (GO) hydrogel (UCN-GH) was prepared by co-assembling of UCN and GO nanosheets via the facile hydrothermal reaction. Characterizations indicated that the addition of UCN significantly decreased the reduction of CO and O-CO related groups of GO during the hydrothermal reaction and introduced amine groups on UCN-GH. The UCN-GH exhibited excellent ability on the co-removal of Cu(II) (q_max = 2.0-2.5 mmol g^-1) and tetracycline (TC) (q_max = 1.2-3.0 mmol g^-1) from water. The adsorption capacities were increased as UCN mass ratio increasing. The mutual effects between Cu(II) and TC were examined through adsorption kinetics and isotherm models. Characterizations and computational chemistry analysis indicated that Cu(II) is apt to coordinate with the amine groups on UCN than with oxygen groups on GO, which accounts for the enhanced adsorption ability of UCN-GH. In the binary system, Cu(II) acts as a bridge between TC and UCN-GH enhanced the removal of TC. The effects of pH and regular salt ions on the removal of Cu(II)/TC were examined. Moreover, the prepared UCN-GH also showed comparable co-adsorption capacities in practical water/wastewater.

A novel Janus sponge fabricated by a green strategy for simultaneous separation of oil/water emulsions and dye contaminants

A novel Janus sponge with the ability to remove complex contaminants from water is reported. Firstly, a superhydrophilic sponge (PA@PEI-sponge) is prepared via synthesizing negatively charged phytic acid@polyethyleneimine (PA@PEI) nanoparticles and assembling them on the surface of polydopamine (PDA) and PEI-modified polyurethane (PU) sponge through electrostatic adsorption. The Janus sponge is generated by modifying one side of the PA@PEI-sponge with PDMS, which exhibits superior separation efficiency and high filtration flux toward both water-in-oil and oil-in-water emulsions due to its multiplex selective wettability and the interconnected and tortuous 3D porous channels. The numerous negatively charged active sites of PA@PEI nanoparticles and PDA layer impart the superhydrophilic PA@PEI-sponge with the removal efficiency of 39.95 ± 0.27% for malachite green (MG) via simple flow-through filtration, which can be improved to 99.92 ± 0.07% by Janus modification. More importantly, the Janus sponge exhibits an excellent treatment capacity for complex mixtures containing emulsified oil and dye, with the separation efficiency above 99.59%. The Janus sponge also demonstrates the effective separation of real industrial wastewater collected from an acrylic dyeing plant. Together with a facile and green preparation strategy, this Janus sponge shows excellent application potential for simultaneous dye removal and oil/water emulsion separation.

Application of activated carbon functionalized with graphene oxide for efficient removal of COVID-19 treatment-related pharmaceuticals from water

Currently, the COVID-19 pandemic has been increasing the consumption of some drugs, such as chloroquine (CQN) and dipyrone (DIP), which are continuously discharged into water resources through domestic sewage treatment systems. The presence of these drugs in water bodies is worrisome due to their high toxicity, which makes crucial their monitoring and removal, especially by means of advanced technologies. Given this scenario, a new adsorbent material was synthesized through the combination of babassu coconut activated carbon and graphene oxide (GAC-GO). This study was evaluated in batch adsorption processes, aiming at the treatment of water contaminated with CQN and DIP. Characterization analyzes using physicochemical and spectroscopic techniques indicated that the GAC-GO functionalization was successfully performed. The equilibrium time of the adsorption process was 18 and 12 h for CQN and DIP, respectively. Kinetic and isothermal data better fitted to pseudo-second-order and Langmuir models for both drugs. Thermodynamic parameters showed that the process is endothermic and the maximum adsorption capacities of CQN and DIP were 37.65 and 62.43 mg g-1, respectively, both at 318 K. The study of the effect of ionic strength, which simulates a real effluent, demonstrated that the synthesized adsorbent has potential application for the treatment of effluents. Furthermore, satisfactory removal rates were verified for the removal of other contaminants in both simple solutions and synthetic mixtures, evidencing the versatile profile of the adsorbent.

Efficient removal of a low concentration of Pb(II), Fe(III) and Cu(II) from simulated drinking water by co-immobilization between low-dosages of metal-resistant/adapted fungus Penicillium janthinillum and graphene oxide and activated carbon

Drinking water safety cannot be overemphasized. Filamentous fungi have many excellent features for metal removal. Both graphene oxide (GO) and activated carbon (AC) are conventional metal adsorbents, but they are not suitable for large-scale use due to high cost. In this study, a low dosage of conidia (2.0 × 10⁴ conidia/mL) of metal-resistant/adapted filamentous fungus Penicillium janthinillum strain GXCR were co-immobilized with a low dosage of 0.5 mg/L GO or 0.5 mg/L AC by embedding in 2% polyvinyl alcohol (PVA)-3% sodium alginate (SA), generating six types of microbead adsorbents (MBAs) to remove metals from a low concentration of either single metal (100 mg/L) or mixed metals (100 mg/L each) of Pb (II), Fe (III) and Cu (II) in drinking water. Fungus GXCR-containing MBAs had higher specific surface areas (SSAs), better mesoporous structures, and a higher removal rate (85-98.99%) of single or mixed metals. Singl-metal adsorptions of MBAs were almost unaffected by temperature changes. MBAs showed a stable removal rate of 87-94% during four cycles of adsorption-desorption of single metal. Single-metal adsorptions were well described by multiple models of Freundlich isotherm with constant values of 0.21-0.432, Langmuir isotherm with constant values of 0.037-0.17, Pseudo-fist-order, Pseudo-second-order, and intra-particle diffusion (IPD). In conclusion, co-immobilization between GXCR, GO and AC can make metal removal more efficient. Adsorption capacity is increased with SSAs but not in the same proportion. Single-metal adsorptions involve multiple mechanisms of monolayer and multilayer adsorptions, external mass transfer, and IPD. IPD is important but not the only one rate-controlling step for single-metal adsorptions.

Effective and Simple NaOH-Modification Method to Remove Methyl Violet Dye via Ipomoea aquatica Roots

In this study, a simple chemical modification was applied to a sustainable and abundantly available resource, kangkong root (KR), to remove methyl violet 2B (MV) dye. The chemically modified adsorbent (NaOH-KR) was obtained using NaOH solution treatment. Batch adsorption experiments were carried out to investigate the effects of pH, ionic strength, contact time, adsorbent dosage, and initial dye concentration. A regeneration experiment was also carried out to assess the potential of reusability. The adsorption process was modelled using various kinetics and isotherm models, whereby the best-fitting models were evaluated by using the coefficient of determination ( $R^2$ ) and error functions. The Sips ( $R^2=0.9714$ , χ2 =0.16) and pseudo-second-order ( $R^2=0.9996$ , ${\chi }^2=0.007$ ) models were identified to best represent the adsorption process. The Sips model predicted a maximum adsorption capacity at 551.5 mg g-1 for NaOH-KR, which is 55% improvement in performance when compared to nonmodified KR. Lastly, the regeneration experiment showed that NaOH-KR was able to maintain reasonable dye removal even after five consecutive cycles of regenerating and reusing.

Influence of the Nanotube Morphology and Intercalated Species on the Sorption Properties of Hybrid Layered Vanadium Oxides: Application for Cesium Removal from Aqueous Streams

The present paper examines the impact that the nanotube morphology and organic or inorganic intercalated species may have on the cesium sorption by layered vanadium oxides prepared with the use of hexadecylamine as a structure-directing agent. The hybrid material represented by a chemical formula of (V₂O₅)(VO₂)_1.03(C₁₆H₃₆N)_1.46(H₂O)_x was achieved through accelerated microwave-assisted synthesis carefully optimized to ensure the best compromise between the scroll-like morphology and the hydrophobic character. To enhance its dispersibility in water, this sample was subsequently modified by progressive replacement of the C₁₆H₃₆N⁺ units by NH₄⁺ cations. The final materials represented a stacking of lamellar sheets with a worse scroll-like morphology. Both the optimization procedure and the template removal were monitored on the basis of scanning and transmission electronic microscopy, X-ray diffraction, infra-red spectroscopy, inductively coupled plasma-optical emission spectrometry, X-ray photoelectron spectroscopy, and elemental analysis, supplemented by adequate simulations methods providing the reference IR spectra and XRD patterns for comparison or the textural parameters of the samples. The comparison of the cesium sorption from either a 4:1 ethanol–water mixture or aqueous solutions pointed toward the solubility of intercalated cations in the bulk solution as the main factor limiting their displacement from the interlayer space by the oncoming cesium ones. The sample obtained after 70% exchange with NH₄⁺ exhibited a maximum sorption capacity of 1.4 mmol g⁻¹ from CsNO₃ aqueous solutions and its retention efficiency remained significant from low-concentration Cs solutions in river or sea water.

Microalgae and bio-polymeric adsorbents: an integrative approach giving new directions to wastewater treatment

This review analyses the account of biological (microalgae) and synthetic (bio-polymeric adsorbents) elements to compass the treatment efficiencies of various water pollutants and mechanisms behind them. While considering pollutant removal, both techniques have their own merits and demerits. Microalgal-based methods have been dominantly used as a biological method for pollutant removal. The main limitations of microalgal methods are capacity, scale, dependence on variables of environment and duration of the process. Biopolymers on the other hand are naturally produced, abundant in nature, environmentally safe and biocompatible with cells and many times biodegradable. Algal immobilization in biopolymers has promoted the reuse of cells for further treatment and protected cells from toxic environment monitoring and controlling the external factors like pH, temperature and salinity can promote the removal process while working with the mentioned technologies. In this review, a mechanistic view of both these techniques along with integrated approaches emphasizing on their loopholes and possibilities of improvement in these techniques is represented. In addition to these, the review also discusses the post-treatment effect on algal cells which are specifically dependent on pollutant type and their concentration. All these insights will aid in developing integrated solutions to improve removal efficiencies in an environmentally safe and cost-effective manner.Novelty statement The main objective of this review is to thoroughly understand the role of micro-algal cells and synthetic adsorbents individually as well as their integrative effect in the removal of pollutants from wastewater. Many reviews have been published containing information related to either removal mechanism by algae or synthetic adsorbents. While in this review we have discussed the agents, algae and synthetic adsorbents along with their limitations and explained how these limitations can be overcome with the integration of both the moieties together in process of immobilization. We have covered both the analytical and mechanistic parts of these technologies. Along with this, the post-treatment effects on algae have been discussed which can give us a critical understanding of algal response to pollutants and by-products obtained after treatment. This review contains three different sections, their importance and also explained how these technologies can be improved in the future aspects.

Magnetic nanoadsorbents for micropollutant removal in real water treatment: a review

Pure water will become a golden resource in the context of the rising pollution, climate change and the recycling economy, calling for advanced purification methods such as the use of nanostructured adsorbents. However, coming up with an ideal nanoadsorbent for micropollutant removal is a real challenge because nanoadsorbents, which demonstrate very good performances at laboratory scale, do not necessarily have suitable properties in in full-scale water purification and wastewater treatment systems. Here, magnetic nanoadsorbents appear promising because they can be easily separated from the slurry phase into a denser sludge phase by applying a magnetic field. Yet, there are only few examples of large-scale use of magnetic adsorbents for water purification and wastewater treatment. Here, we review magnetic nanoadsorbents for the removal of micropollutants, and we explain the integration of magnetic separation in the existing treatment plants. We found that the use of magnetic nanoadsorbents is an effective option in water treatment, but lacks maturity in full-scale water treatment facilities. The concentrations of magnetic nanoadsorbents in final effluents can be controlled by using magnetic separation, thus minimizing the ecotoxicicological impact. Academia and the water industry should better collaborate to integrate magnetic separation in full-scale water purification and wastewater treatment plants.

Insight into Cr(VI) biosorption onto algal-bacterial granular sludge: Cr(VI) bioreduction and its intracellular accumulation in addition to the effects of environmental factors

Hexavalent chromium (Cr(VI)) is one of the typical heavy metals that pose a great threat to the environment. As a novel biotechnology, algal-bacterial aerobic granular sludge (AGS) possesses the merits of both bacterial AGS and algae. This study firstly evaluated Cr(VI) removal via biosorption by algal-bacterial AGS under different operation conditions and then some environmental factors. Results show that the highest Cr(VI) reduction (99.3%) and total Cr removal (89.1%) were achieved within 6 h at pH 2 and 6, respectively. The coexisting oxyanions exhibited slight effects, while both tested natural organic matters (humic acid and tannic acid) and carbon sources promoted Cr(VI) reduction at some appropriate concentrations. The coexistence of metal cations favored Cr(VI) reduction, achieving the highest enhancement of 8.1% by Cu²⁺ at 5 mg/L, while the total Cr removal was suppressed to some extent. Salinity > 5 g/L severely inhibited both Cr(VI) reduction and total Cr removal. Moreover, the loaded Cr in algal-bacterial AGS was found to be almost in the form of Cr(III), with 66.8% being contributed by intracellular accumulation. This work suggests that Cr(VI) reduction and intracellular accumulation are the main mechanisms involved in Cr(IV) biosorption onto algal-bacterial AGS.

Process optimization and enhancement of pesticide adsorption by porous adsorbents by regression analysis and parametric modelling

In the present study, the adsorptive removal of organophosphate diazinon pesticide using porous pumice adsorbent was experimentally investigated in a batch system, modelled and optimized upon response surface methodology (RSM) and artificial neural network-genetic algorithm (ANN-GA), fitted to isotherm, kinetic and thermodynamic models. The quantification of adsorbent elements was determined using EDX. XRD analysis was utilized to study the crystalline properties of adsorbent. The FT-IR spectra were taken from adsorbent before and after adsorption to study the presence and changes in functional groups. The constituted composition of the adsorbent was determined by XRF. Also, the ionic strength and adsorbent reusability were explored. The influences of operational parameters like pH, initial pesticide concentration, adsorbent dosage and contact time were investigated systematically. ANN-GA and RSM techniques were used to identify the optimal process variables that result in the highest removal. Based on the RSM approach, the optimization conditions for maximum removal efficiency is obtained at pH = 3, adsorbent dosage = 4 g/L, contact time = 30 min, and initial pesticide concentration = 6.2 mg/L. To accurately identify the parameters of nonlinear isotherm and kinetic models, a hybrid evolutionary differential evolution optimization (DEO) is applied. Results indicated that the equilibrium adsorption data were best fitted with Langmuir and Temkin isotherms and kinetic data were well described by pseudo-first and second-order kinetic models. The thermodynamic parameters such as entropy, enthalpy and Gibbs energy were evaluated to study the effect of temperature on pesticide adsorption.