Effective and simultaneous removal of organic/inorganic arsenic using polymer-based hydrated iron oxide adsorbent: Capacity evaluation and mechanism

Efficient roxarsone degradation by low-dose peroxymonosulfate with the activation of recycling iron-base composite material: Critical role of electron transfer

Pollutant degradation via electron transfer based on advanced oxidation processes (AOPs) provides an economical and energy-efficient method for pollution control. In this study, an iron-rich waste, heating pad waste (HPW), was recycled as a raw material, and a strong magnetic catalyst (Fe-HPW) was synthesized at high temperature (900 °C). Results showed that in the constructed Fe-HPW/PMS system, effective roxarsone (ROX) degradation and TOC removal (72.54%) were achieved at a low-dose of oxidant (PMS, 0.05 mM) and catalyst (Fe-HPW, 0.05 g L-1), the ratio of PMS to ROX was only 2.5:1. In addition, the released inorganic arsenic was effectively removed from the solution. The analysis of the experimental results showed that ROX was effectively degraded by forming PMS/catalyst surface complexes (Fe-HPW-PMS*) to mediate electron transfer in the Fe-HPW/PMS system. Besides, this system performed effective ROX degradation over a wide pH range (pH=3-9) and showed high resistance to different water parameters. Overall, this study not only provides a new direction for the recycling application of HPW but also re-emphasizes the neglected nonradical pathway in advanced oxidation processes.

Adsorption effects of electron scavengers and inorganic ions on catalysts for catalytic oxidation of sulfamethoxazole in radiation treatment

This study aimed to investigate adsorption effects of electron scavengers (H2O2 and S2O82-) on oxidation performance for mineralization of sulfamethoxazole (SMX) in radiation treatment using catalysts (Al2O3, TiO2). Hydrogen peroxide (H2O2, 1 mM) as an electron scavenger showed weak adsorption onto catalysts (0.012 mmol g-1-Al2O3 and 0.004 mmol g-1-TiO2, respectively), leading to an increase in TOC removal efficiency of SMX within the absorbed dose of 30 kGy by 12.3% with Al2O3 and by 8.0% with TiO2. The weak adsorption of H2O2 onto the catalyst allowed it to act as an electron scavenger, promoting indirect decomposition reactions. However, high adsorption of S2O82- (1 mM) onto Al2O3 (0.266 mmol g-1-Al2O3) showed a decrease in TOC removal efficiency of SMX from 76.2% to 30.2% within the absorbed dose of 30 kGy. The high adsorption of S2O82- onto the catalyst inhibited direct decomposition reaction by reducing adsorption of SMX on catalysts. TOC removal efficiency for Al2O3 without electron scavengers in an acidic condition was higher than that in a neutral or alkaline condition. However, TOC removal efficiency for Al2O3 with S2O82- was higher in a neutral condition than in other pH conditions. This indicates that the pH of a solution plays a critical role in the catalytic oxidation performance by determining surface charges of catalysts and yield of reactive radicals produced from water radiolysis. In the radiocatalytic system, H2O2 enhances the oxidation performance of catalysts (Al2O3 and TiO2) over a wide pH range (3-11). Meanwhile, S2O82- is not suitable with Al2O3 in acidic conditions because of its strong adsorption onto Al2O3 in this study.

New design to enhance phosphonate selective removal from water by MOF confined in hyper-cross-linked resin

Although polymeric anion exchange resins can remove phosphonates, they lack selectivity for target phosphonates and are susceptible to interference by anions and other substances. Here, we developed a novel strategy via confining MIL-101(Fe)-NH2 inside commercial resins IRA-900 for high-efficient and precise phosphonate removal, accompanying with the improvement of the stability and recovery of MIL-101(Fe)-NH2. The obtained nanocomposite MIL-101(Fe)-NH2@IRA-900 (MFNI) exhibited significantly enhanced phosphonate removal in the presence of competing anions (Cl-, SO42-, NO3- and CO32-) and natural organic matter (humic acid) at high concentrations (2-4 times of phosphonate concentration). Moreover, MFNI displayed the highest phosphonate adsorption capacity (12.9 mg P/g) and the fastest adsorption kinetics (120 min) than hydrated ferric oxides modified IRA-900 (HFOI) (6.7 mg P/g, 180 min), MIL-101(Fe)-NH2 (7.6 mg P/g, 240 min) and IRA-900 (5.6 mg P/g, 360 min). Such higher adsorption affinity and anti-interference ability came from the synergistic effect of the host IRA-900 (hydrogen-bond interaction and electrostatic attraction) and the embedded MIL-101(Fe)-NH2 (ligand exchange). The depleted MFNI could be regenerated with a binary NaOH-NaCl solution and reused without significant loss of capacity. Column adsorption runs by using MFNI indicated the fresh MFNI could achieve 100 % removal of PPOA in 10.5 h continuously feeding, which offered the possibility of achieving potential large-scale applications. In general, a new MOF-confined design approach was practiced to achieve selective elimination of phosphates and to improve the stability and recovery of MOF.

Remarkable adsorption of As(V) by Fe3+ and Mg2+ modified alginate porous beads (Fe/Mg-SA) via a facile method

Although sodium alginate (SA) is frequently utilized because of its good gelling properties, the substance's dearth of adsorption active sites prevents it from effectively removing heavy metals. Herein, SA was used as the base material to form a cross-linked structure with Fe3+ and Mg2+, and gel beads with a diameter of 2.0 ± 0.1 mm with specific adsorption on As(V) were synthesized as adsorbent (Fe/Mg-SA). Fe/Mg-SA was systematically characterized, and its adsorption properties were investigated by varying several conditions. Fe/Mg-SA had a wide pH application range. The adsorption kinetics revealed that a quasi-secondary kinetic model was followed. The adsorption process is linked to the complexation of hydroxyl and AsO43-, chemisorption predominated the adsorption process. The maximal adsorption capacity of Fe/Mg-SA is determined by fitting the Langmuir model to be 37.4 mg/g. Compared to other adsorbents, it is simpler to synthesis, more effective and cheaper. Each treatment of 1 m3 wastewater of Fe/Mg-SA only costs ¥ 38.612. The novel gel beads synthesized provides a better option for purifying groundwater contaminated with As(V).

Isolation and characterisation of Fe(II)-oxidising bacteria and their application in the removal of arsenic in an aqueous solution

Arsenic (As) is a toxic metalloid disseminated in water, soil, and air. Arsenic contamination is currently a major public health concern. This study investigated arsenic removal by Fe(II)-oxidising bacteria in an aqueous solution. A bacterial strain, Z1, isolated from concentrated sludge, was identified as Sphaerotilus natans based on microscopic morphology, culture characteristics, and 16s rRNA gene sequences. After arsenic-resistant acclimation, Sphaerotilus natans Z1 successfully survived and propagated in high arsenic conditions (100 mg·L-1 As(V) or As(III)). To a certain extent, the isolated strain could decrease the concentration of As(III)/As(V) by biosorption under organic substance supply. Partial As(V) could be reduced to As(III) due to cytoplasmic arsenic reduction of bacteria. In addition, ferrihydrite, one of the iron oxides, was formed by the mediation of Sphaerotilus natans in the Winogradsky medium. Most of As(III)/As(V) could be effectively removed by sorbing onto the resultant ferrihydrite mineral. Thus, iron oxide minerals facilitated by Sphaerotilus natans may be an alternative remediation strategy for scavenging arsenic in the water environment.

The interfacial behaviors of different arsenic species on polyethylene mulching film microplastics: Roles of the plastic additives

Plastic additives widely existed in plastic mulching films, but their roles in microplastics (MPs) derived from these plastics as vectors of pollutants were not clear. This work clarified the role of plastic additives on the sorption-desorption behaviors of four arsenic species (arsenite (As(Ⅲ)), arsenate (As(Ⅴ)), roxarsone (ROX), and p-arsanilic acid (p-ASA)) on/from virgin polyethylene (V-PE), white PE mulching film (W-PE, with Si-containing additives), and black PE mulching film (B-PE, with CaCO₃ and TiO₂ additives) MPs. The maximum sorption amounts of arsenic species on V-PE (3.33-20.10 mg/kg) and W-PE MPs (4.78-21.93 mg/kg) had no significant difference, while those on B-PE (43.02-252.19 mg/kg) facilitated by its additives were up to one order of magnitude greater than V-PE or W-PE (p < 0.05). Desorption hysteresis index (HI) indicated the irreversible arsenic sorption on three PE MPs, especially for B-PE containing additives that can co-precipitate and complex with arsenicals. The effects of pH, humic substances, and coexisting anions on arsenic sorption by B-PE were more obvious than that by V-PE or W-PE MPs, attributing to electrostatic interaction enhanced by CaCO₃ and TiO₂ additives. This work provides theoretical basis for migration of arsenic species on MPs containing plastic additives and their potential environmental risk assessment.

Utilization of Bioflocculants from Flaxseed Gum and Fenugreek Gum for the Removal of Arsenicals from Water

Mucilage-based flocculants are an alternative to synthetic flocculants and their use in sustainable water treatment relates to their non-toxic and biodegradable nature. Mucilage extracted from flaxseed (FSG) and fenugreek seed (FGG) was evaluated as natural flocculants in a coagulation-flocculation (CF) process for arsenic removal, and were compared against a commercial xanthan gum (XG). Mucilage materials were characterized by spectroscopy (FT-IR, ¹³C NMR), point-of-zero charge (pH_pzc) and thermogravimetric analysis (TGA). Box-Behnken design (BBD) with response surface methodology (RSM) was used to determine optimal conditions for arsenic removal for the CF process for three independent variables: coagulant dosage, flocculant dosage and settling time. Two anionic systems were tested: S1, roxarsone (organic arsenate 50 mg L^-1) at pH 7 and S2 inorganic arsenate (inorganic arsenate 50 mg L^-1) at pH 7.5. Variable arsenic removal (RE, %) was achieved: 92.0 (S1-FSG), 92.3 (S1-FGG), 92.8 (S1-XG), 77.0 (S2-FSG), 69.6 (S2-FGG) and 70.6 (S2-XG) based on the BBD optimization. An in situ kinetic method was used to investigate arsenic removal, where the pseudo-first-order model accounts for the kinetic process. The FSG and FGG materials offer a sustainable alternative for the controlled removal of arsenic in water using a facile CF treatment process with good efficiency, as compared with a commercial xanthan gum.

Arsenic removal performance and mechanism from water on iron hydroxide nanopetalines

Human health has been seriously endangered by arsenic pollution in drinking water. In this paper, iron hydroxide nanopetalines were synthesized through a precipitation method using KBH₄ and their performance and mechanism of As(V) and As(III) removal were investigated. The prepared material was characterized by SEM-EDX, XRD, BET, zeta potential and FTIR analyses. Batch experiments indicated that the iron hydroxide nanopetalines exhibited more excellent performance for As(V) and As(III) removal than ferrihydrite. The adsorption processes were very fast in the first stage, followed a relatively slower adsorption rate and reached equilibria after 24 h, and the reaction could be fitted best by the pseudo-second order model, followed by the Elovich model. The adsorption isotherm data followed to the Freundlich model, and the maximal adsorption capacities of As(V) and As(III) calculated by the Langmuir model were 217.76 and 91.74 mg/g at pH 4.0, respectively, whereas these values were 187.84 and 147.06 mg/g at pH 8.0, respectively. Thermodynamic studies indicated that the adsorption process was endothermic and spontaneous. The removal efficiencies of As(V) and As(III) were significantly affected by the solution pH and presence of PO₄^3- and citrate. The reusability experiments showed that more than 67% of the removal efficiency of As(V) could be easily recovered after four cycles. The SEM and XRD analyses indicated that the surface morphology and crystal structure before and after arsenic removal were stable. Based on the analyses of FTIR, XRD and XPS, the predominant adsorption mechanism was the formation of inner-sphere surface complexes by the surface hydroxyl exchange reactions of Fe-OH groups with arsenic species. This research provides a new strategy for the development of arsenic immobilization materials and the results confirm that iron hydroxide nanopetalines could be considered as a promising material for removing arsenic from As-contaminated water for their highly efficient performance and stability.

Application of iron oxyhydroxide to stabilize As(V) and phenylarsonic acid in contaminated soil: adsorption and the relevance to bioavailability

The leaked arsenic-containing chemical warfare agent has caused severe contamination to the surrounding soil and water. In this study, iron oxyhydroxide (FeOOH) with different crystalline phases was used to stabilize arsenic. The results revealed that α/β- mixed crystalline iron oxyhydroxide (MIX-FeOOH) had better adsorption performance for As(V) and phenylarsonic acid (PAA) in water, with the adsorption capacity 71.4 and 54.7 mg g^-1 at 50 mg L^-1 equilibrium concentration, respectively. The adsorption mechanism was proved to be inner-sphere complexation, electrostatic interaction, and hydrogen bonding. Meanwhile, the oxygen vacancies on FeOOH could increase the isoelectric point and further promote the adsorption capacity through inner-sphere complexation. In arsenic contaminated soil, when the addition amount of MIX-FeOOH was 5%, the bioavailability of arsenic in As(V) and PAA contaminated soil was significantly reduced after 28 days, and the stabilization rate reached 77.2% and 76.5%, respectively. After 7 days of remediation, 17.1% and 11.9% of the most mobile portions of As(V) and PAA could be converted into poorly mobile portions, respectively. The stabilization mechanism includes inner-sphere complexation, mineral adsorption, and coprecipitation. In summary, this study can provide technical support for the remediation practice of arsenic-containing warfare agent contaminated sites.

The Role of Conventional Methods and Artificial Intelligence in the Wastewater Treatment: A Comprehensive Review

Water pollution is a severe health concern. Several studies have recently demonstrated the efficacy of various approaches for treating wastewater from anthropogenic activities. Wastewater treatment is an artificial procedure that removes contaminants and impurities from wastewater or sewage before discharging the effluent back into the environment. It can also be recycled by being further treated or polished to provide safe quality water for use, such as potable water. Municipal and industrial wastewater treatment systems are designed to create effluent discharged to the surrounding environments and must comply with various authorities’ environmental discharge quality rules. An effective, low-cost, environmentally friendly, and long-term wastewater treatment system is critical to protecting our unique and finite water supplies. Moreover, this paper discusses water pollution classification and the three traditional treatment methods of precipitation/encapsulation, adsorption, and membrane technologies, such as electrodialysis, nanofiltration, reverse osmosis, and other artificial intelligence technology. The treatment performances in terms of application and variables have been fully addressed. The ultimate purpose of wastewater treatment is to protect the environment that is compatible with public health and socioeconomic considerations. Realization of the nature of wastewater is the guiding concept for designing a practical and advanced treatment technology to assure the treated wastewater’s productivity, safety, and quality.

CTAB-functionalized δ-FeOOH for the simultaneous removal of arsenate and phenylarsonic acid in phenylarsenic chemical warfare

This study prepared a cetyltrimethylammonium bromide (CTAB) functionalized δ-FeOOH using the coprecipitation method to remove arsenate and phenylarsonic acid in water polluted by phenylarsonic chemical warfare agents. Under neutral conditions, the adsorption capacity for arsenate and phenylarsonic acid was 45.7 and 85.3 mg g^-1, respectively. The adsorption process conformed to the pseudo-second-order kinetics and Freundlich isothermal adsorption model, and the adsorption was spontaneous and endothermic. The CTAB-functionalized δ-FeOOH could effectively resist the interference of coexisting anions except for CO₃^2-, SiO₃^2- and PO₄^3-. Furthermore, the adsorption mechanism was proposed by combining the adsorption experimental results, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory analyses. The results showed that the adsorption of arsenate by the CTAB-functionalized δ-FeOOH was mainly through the formation of bidentate-dinuclear inner-sphere complexes and electrostatic interactions. While for phenylarsonic acid, the formation of monodentate-mononuclear inner-sphere complexes on (100) and (110) crystal facets, and the formation of bidentate-dinuclear inner-sphere complexes on the (002) crystal facet, as well as hydrogen bonding, electrostatic interaction, and π-hydrophobic interaction between organic compounds were the primary mechanism. Moreover, the CTAB-functionalized δ-FeOOH could maintain about 60% of the adsorption capacity for the two pollutants after five cycles. Overall, CTAB-functionalized δ-FeOOH has good potential for the remediation of inorganic and organic arsenic-contaminated water bodies.

Multifunctional hybrid membranes for photocatalytic and adsorptive removal of water contaminants of emerging concern

This work focuses on the combination of multifunctional photocatalytic and adsorbent materials in a unique polymeric membrane. For this purpose, Au/TiO₂ and Y₂(CO₃)₃ nanoparticles were immobilised onto a poly (vinylidene fluoride-hexafluoropropylene), (PVDF-HFP) membrane, and the physical-chemical characterisation of these materials was performed, as well as pollutant removal efficiency. An efficient TiO₂ functionalisation with gold nanoparticles was achieved, endowing these particles with the capability to absorb visible radiation absorption. A favourable porous structure was obtained for the membranes, with an average pore size of 4 μm, and the nanoparticles immobilisation did not alter the chemical properties of the polymeric membrane. The produced hybrid materials, including both the Au/TiO₂ and Y₂(CO₃)₃ nanoparticles, presented an efficiency of 57% in the degradation of norfloxacin (5 mg/L) under ultraviolet radiation for 120 min, 80% under visible radiation for 300 min, and 58% in arsenic adsorption for 240 min. These membranes represent a new multifunctional platform for removing several pollutants, which may allow their incorporation in more efficient and less energy-consuming water treatment processes favouring its application, even in low energy resources countries.

Arsenic removal by manganese-doped mesoporous iron oxides from groundwater: Performance and mechanism

FeMn bimetallic oxides have been widely used in catalytic adsorption due to their large pore size, large specific surface area and mesoporous structure, which have great potential for high As groundwater remediation. In this study, FeMn composite oxide was synthesized by template-free route and forming mesopores through high temperature calcination, and its efficiency and mechanism for As removal were subsequently investigated. The results showed that the different Fe/Mn molar ratios and calcination temperatures have important effect on FeMn composite oxides performance. For all synthesized materials, the largest specific surface area is 388.6 m²/g of Fe₁Mn₁-300. The maximum As absorption capacity was also reached by Fe₁Mn₁-300, which is 59.44 mg/g for As(III) and 31.68 mg/g for As(V), respectively. As removal efficiency was further evaluated through batch adsorption experiments conducted with five variables, initial As concentration, adsorption equilibrium time, pH, solid-to-liquid ratio, and competitive ions. The adsorption capacity of the material reaches to the maximum when the initial As concentration is 40 mg/L, and that for As(III) and As(V) is 74.05 and 38.09 mg/g, respectively. When the pH rises, the adsorption capacity generally shows a decreasing trend, thus acidic conditions are more conducive to the adsorption reaction. The optimum solid-to-liquid ratios for removal 10 mg/L of As(III) and As(V) are 0.3 mg/L and 1 mg/L, respectively. The order of competitive ions effects on As removal is: PO₄^3- > HCO₃^- > SO₄^2- ≈ NO₃^- ≈ Cl^-. The adsorption mechanisms for As by FeMn composite oxides included adsorption, co-precipitation and oxidative chelation, which was a combination of physical and chemical process.

Effectively remove p-arsanilic acid from water over amphiphilic amino modified collagen fiber

Efficient and rapid removal of p-arsanilic acid (p-ASA) in water is very important in environmental protection and human health, however it is still a severe challenge in actual engineering. Herein, a novel sorbent (CF-PEI) was successfully fabricated by simply modifying the amphiphilic skin collagen fiber (CF) substrate with Polyethylenimine (PEI). The as-prepared CF-PEI exhibits high-efficiency adsorption for negatively charged p-ASA with aromatic rings due to the introduction of amino groups and the existence of hydrophobic bands, and the maximum adsorption capacity of CF-PEI for p-ASA was high up to 285.71 mg g^-1. In addition, the adsorption mechanism of CF-PEI on p-ASA mainly includes electrostatic interaction, hydrogen bond and amphiphilicity. The multi-level all-fiber structure of CF makes it mainly focus on surface mass transfer with short mass transfer distance, and its capillary drainage effect can realize large flow and rapid separation. CF-PEI based on CF can realize the ability to separate low-concentration p-ASA with high flow rate and high efficiency. The effective processing volume was 12.5 L g^-1 when the separation flux reached as high as 9931.27 L m^-2 h^-1. Notably, the p-ASA adsorbed on CF-PEI was almost completely eluted by NaOH (0.5 mol L^-1). The adsorbent is convenient to prepare, recyclable, high in efficiency, and has a great application prospect in removing organic micro-pollutants.

Improved utilization of active sites for phosphorus adsorption in FeOOH/anion exchanger nanocomposites via a glycol-solvothermal synthesis strategy

Metal oxide/hydroxide-based nanocomposite adsorbents with porous supporting matrices have been recognized as efficient adsorbents for phosphorus recovery. Aiming at satisfying increasingly restrictive environmental requirements involving improving metal site utilization and lowering metal leakage risk, a glycol-solvothermal confined-space synthesis strategy was proposed for the fabrication of FeOOH/anion exchanger nanocomposites (Fe/900s) with enhanced metal site utilization and reduced metal leakage risk. Compared to composites prepared using alkaline precipitation methods, Fe/900s performed comparably, with a high adsorption capacity of 19.05 mg-P/g with an initial concentration of 10 mg-P/L, a high adsorption selectivity of 8.2 mg-P/g in the presence of 500 mg-SO₄^2-/L, and high long-term resilience (with a capacity loss of ~14% after five cycles), along with substantially lower Fe loading amount (4.11 wt.%) and Fe leakage percentage. Mechanistic investigation demonstrated that contribution of the specific FeOOH sites to phosphate adsorption increased substantially (up to 50.97% under the optimal conditions), in which Fe(III)-OH was the dominant efficient species. The side effects of an excessively long reaction time, which included quaternary ammonium decomposition, FeOOH aggregation, and Fe(III) reduction, were discussed as guidance for optimizing the synthesis strategy. The glycol-solvothermal strategy provides a facile solution to environmental problems through nanocrystal growth engineering in a confined space.

Simultaneous decontamination of arsenite and antimonite using an electrochemical CNT filter functionalized with nanoscale goethite

The co-presence of arsenic (As) and antimony (Sb) in water bodies has been commonly reported. The toxicity of As and Sb varies with different speciation. Herein, we designed a dual-functional electrochemical filter toward "one-step" detoxification and sequestration of highly toxic As(III) and Sb(III). The key to this technology is a functional anodic filter consists of nanoscale goethite and carbon nanotubes (CNT). Results showed that 97.9% As(III) and 91.9% Sb(III) transformation and 86.4% As_total and 70.1% Sb_total removal efficiency can be obtained over 2 h continuous filtration under optimized conditions. The As_total removal kinetics and efficiency enhanced with flow rate and applied voltage (e.g., the As_total removal efficiency increased from 62.9% at 0 V to 86.4% at 2.5 V). This enhancement in kinetics and efficiency can be explained by the synergistic effects of the flow-through design, plentiful exposed sorption sites, electrochemical reactivity, and nanoscale goethite. Moreover, the proposed technology works effectively across a wide pH range. Only negligible inhibition was observed in the presence of nitrate, chloride, and carbonate. Exhausted hybrid filters can be effectively regenerated by using chemical wash with NaOH solution. This study not only revealed the different adsorption behaviors of As(III) and Sb(III) on the hybrid filters, but also provided new insights into rational design of continuous-flow filters toward simultaneous decontamination of As(III) and Sb(III).

Development of novel multifunctional adsorbent by effectively hosting both zwitterionic surfactant and hydrated ferric oxides in montmorillonite

Intercalating various functional species into the interlayer space is an effective strategy to multi-functionalize 2D materials (e.g., montmorillonite, Mnt), but general limitations have emerged therefrom: (1) various intercalated species compete for the limited interlayer space, and (2) the neighboring intercalated species probably inhibit each other's reactivity. Herein, we have synthesized a novel Mnt-based multifunctional adsorbent (HFO-AZ16Mnt) via intercalation of zwitterionic surfactant (Z16), acid activation by chloric acid, and introduction of hydrated ferric oxides (HFOs). The acid activation can lead to formation of porous nanosilica, which serves as the new active sites for supporting HFO nanoparticles. Employing tetrachloroferrate (FeCl₄^-) as an anionic precursor of HFOs can help preserve the sulfonyl group (SO₃^-) of Z16 from being electrostatically occupied during the HFO introduction. As a result, HFO-AZ16Mnt can separately and effectively host Z16 and HFOs. The unique structure endows HFO-AZ16Mnt with the efficiency on simultaneous removal of hydrophobic organic contaminants, oxyanions, and heavy metal cations (nitrobenzene, phosphate, and Cd(II), respectively in this study) from water. Particularly, HFO-AZ16Mnt exhibits impressive capacity towards Cd(II) in both the single- (26.1 mg/g) and the multi-contaminant system (30.6 mg/g). This work has demonstrated a new strategy to multi-functionalize Mnt, and provided a promising novel Mnt-based multifunctional adsorbent for simultaneous and effective removal of organic and inorganic contaminants from water.

Porous biochar-supported MnFe2O4 magnetic nanocomposite as an excellent adsorbent for simultaneous and effective removal of organic/inorganic arsenic from water

To solve the problem of organic and inorganic arsenic species contamination in drinking water and/or wastewater, porous biochar-supported MnFe₂O₄ magnetic nanocomposite (BC-MF) was successfully fabricated and used as an excellent adsorbent for simultaneous removal of p-ASA and As(V) from water environment. This obtained BC-MF displayed remarkable adsorption performance for both p-ASA and As(V) removal at acidic and neutral pH (3-7), and di-anionic and mono-anionic species of p-ASA and As(V) facilitated the adsorption process. Specifically, BC-MF exceeded some reported adsorbents, and the adsorption capacities of p-ASA and As(V) were approximately 105 and 90 mg/g at a 10 μg/L equilibrium concentration. Satisfactory adsorption behavior including adsorption isotherms, competitive ions, humic acid (HA), and regeneration/reusability property in single and binary systems demonstrated the BC-MF can improve the potential application for arsenic-containing wastewater remediation. Proposed adsorption mechanism indicated that electrostatic interaction and surface complexation were involved the p-ASA and As(V) immobilization, whereas hydrogen bonding and π-π interactions may also contribute to the p-ASA removal. Additionally, the prominent sequestration p-ASA and As(V) performance in different water matrix and fixed-bed column studies indicated that BC-MF was a promising nanocomposite for simultaneously removal of organic and inorganic arsenic species in practical wastewater treatment.

Strong Adsorption of Phosphorus by ZnAl-LDO-Activated Banana Biochar: An Analysis of Adsorption Efficiency, Thermodynamics, and Internal Mechanisms

Zn-Al layered bimetallic composites were prepared by ethanol strengthening and co-precipitation using banana straw as a raw material. A high-efficiency phosphorus adsorbent (ZnAl-LDO-BC) was obtained by calcination at a high temperature. The kinetics and thermodynamics of phosphorus adsorption on ZnAl-LDO-BC were then studied. The results showed that the adsorption process of ZnAl-LDO-BC corresponds with the pseudo-second-order (PSO) kinetic equation and the Langmuir model. The theoretical maximum adsorption capacity of ZnAl-LDO-BC is 111.11 mg/g (at 45 °C, 500 mg/L phosphorus initial concentration). The influence of anions on phosphorus adsorption decreased in strength in the following order: CO₃ ^2- > SO₄ ^2- > NO₃ ^-. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) were used to characterize the adsorption of phosphorus on ZnAl-LDO-BC and showed that ZnAl-LDO-BC can efficiently adsorb phosphorus. The adsorption mechanism utilizes both O-H and C-H on the surface of ZnAl-LDO-BC for the adsorption of PO₄ ^3-, forming Zn₃(PO₄)₂·₄H₂O via complexation precipitation; additionally, biochar surface adsorption and interlayer adsorption are indispensable forms of phosphate adsorption. With the systematic study of phosphorus adsorption by ZnAl-LDO-BC, a novel green technology was developed for addressing phosphorus pollution.

Excellent selectivity and high capacity of As (V) removal by a novel lignin-based adsorbent doped with N element and modified with Ca2

As one of the most significant natural polymer with the highest annual yield, lignin has been applied in the treatment of wastewater to remove heavy metal ions. However, there are still some shortages, such as low reactivity, difficulties in adsorbing oxyanions and low selectivity on specific oxyanions. To improve its adsorption properties, a novel lignin-based adsorbent was prepared in this study, doped with nitrogen by Mannich reaction, using triethylenetetramine (TETA) as N source, and further modified with Ca²⁺. The adsorption of Ca, N-co-doped lignin (Ca@N-Lig) for As (V), Cr (VI) and P (V) was studied. The Ca@N-Lig shows high capacity, excellent selectivity and prominent regeneration ability for As (V) adsorption. The adsorption of Ca@N-Lig for As (V) followed the Langmuir isotherm model and the pseudo-second-order kinetics model, yielding a maximum adsorption capacity of 681.59 mg·g^-1 and a fast adsorption equilibrium within 30 min. Ca@N-Lig has an excellent regeneration ability on the adsorption of As (V) with a decrease of about 15.60% after 5 adsorption/desorption cycles. This study offers an efficient way to remove As (V) from polluted water.

Simultaneous removal of organics and heavy metals from industrial wastewater: A review

The co-existence of heavy metals and organics in industrial effluents is a prevalent problem. These pollutants usually have dissimilar compositions and properties, making their complete removal very tedious even with the use of conventional methods. In some cases, organics and heavy metals usually exist in a mixed matrix in industrial wastes. This poses harmful health risks to humans, aquatic lives and the entire ecosystem, because majority of these mixed pollutants amass in water in concentrations which are more than the permissible discharge limits in the environment. Therefore, it is necessary to remove these pollutants in order to prevent them from contaminating both the surface and ground water. Although, the removal of organic compounds and heavy metals (such as Hg, Pb, Cd, As and Cr) could be easily achieved individually, however, these pollutants exist together in many industrial effluents and even in surface waters. Hence the complete removal of these pollutants concurrently in a polluted system is the focus of this study. Several technologies have been used for the simultaneous removal of organics and heavy metal pollutants from water, which includes adsorption, ion exchange, photocatalysis, and coagulation. The success of these techniques depends on the water matrices and the choice of water treatment media such as adsorbents, resins, photocatalysts, and coagulants. The advantages and limitations of these technologies together with their respective mathematical modelling is critically examined in this review. Finally, the effect of joint existence of organic pollutants and heavy metals on the removal efficiency were examined in addition to the mathematical models that discusses the mechanisms of their combine elimination.

Removal and Oxidation of As(III) from Water Using Iron Oxide Coated CTAB as Adsorbent

Iron oxides such as magnetite and maghemite coated with cetyltrimethylammonium bromide (CTAB) are very promising materials for wastewater treatment because iron oxide can be easily separated from solutions using the magnetic separation procedure Iron oxide (IO) coated CTAB was synthesized by an adapted co-precipitation method. In the present study, the IO-CTAB was used for removing arsenic from water for the first time. In the present study, the performance of iron oxide coated CTAB biocomposites as an adsorbent for arsenic removal from aqueous solutions was examined. X-ray diffraction (XRD) analysis and the results revealed a cubic phase Fd-3 m of Fe₃O₄ with lattice a = 8.40 Å and average crystal size equal to 17.26 ± 3 nm. The mean particle size calculated from transmission electron microscopy (TEM) was 19.86 ±1.7 nm. The results of the adsorption batch experiments and the data determined using the Langmuir and Freundlich models emphasized that IO-CTAB nanoparticles were favorable for the adsorption of As(III) ions from aqueous solutions. Ultrasound measurements have shown that IO-CTAB is a cost-effective biocomposite for removing arsenic from contaminated solutions. Moreover, x-ray photoelectron spectroscopy (XPS) has shown that during the process of arsenic absorption, there is oxidation from As(III) to As(V), which leads to a decrease in toxicity during this process. The results of the cytotoxic assays confirmed that the IO-CTAB nanoparticles did not induce any morphological changes in the HeLa cells and did not affect their proliferation after 24 h of incubation.