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The toxic heavy metals contamination in water bodies is one of the major concerns in many countries. Copper and lead are the two common toxic metals present in aquatic environments due to their extensive usage in various industries for diverse applications. The present study deals with the removal of these two toxic heavy metal ions using activated bentonite-alginate (ABn-AG) composite beads which are easily separated and recovered after adsorption reaction. Composite beads were prepared by adapting the ionic gelation method and the materials; i.e., raw bentonite (BnR), activated bentonite (ABn) and ABn-AG were characterized by XRD, BET surface area, TGA-DTA, FT-IR, SEM analyses. The nitrogen adsorption–desorption isotherm obtained for the materials were the type IV isotherm with characteristics H3 hysteresis loops indicating the presence of mesopores with slit-shaped pores. Batch experiments showed that reasonably high percent removal was achieved even at highly acidic conditions, i.e., 58% of Cu2+and 77% of Pb2+were removed at pH 2.0. The removal was fast during the initial contact time and the adsorption data obtained at various contact time were fit well to the pseudo-second order kinetic model. The maximum sorption capacity for Cu2+ was found to be 17.30 mg/g whereas Pb2+ was found to be 107.52 mg/g. The presence of MgCl2, NaCl and KCl did not cause significant influence on the removal of Cu2+ and Pb2+ using ABn-AG. Binary adsorption study suggested that Cu2+ and Pb2+ were removed through different binding sites present in ABn-AG. Reusability test showed that removal of Cu2+ and Pb2+ decreased by 10% only after the same material was reused for 5 times indicating that ABn-AG is a highly robust material and can be reuse for several times without losing its efficiency. Thus, this study suggested that ABn-AG composite beads can be employed as an efficient adsorbent for the removal of Cu2+ and Pb2+ from aqueous waste.

Widespread application of pesticides in agriculture results in contamination of water sources with such compounds. Diazinon is a major environmental challenge in Iran since it is one of the most commonly used pesticides with adverse effects on human health. Therefore, the current study aimed at fabricating and modifying electrospun nanofibrous membrane (ENM) using iron oxide nanoparticles, and investigating its efficiency in removing diazinon from aqueous environments. The current study investigated the effect of different parameters such as nanoparticle concentration in the membrane (0.01, 0.1, and 1%), and soluble parameters such as diazinon concentration (10, 20, 30, and 40 mg/l), pH (5, 7, and 9), and flux in the removal of diazinon from aqueous solutions. The characteristics of ENM were determined by FTIR, SEM, and XRD analysis, and results showed that, the pure nanofibrous membrane was uniform with mean diameter of 180 nm and porosity of 79%. The results also showed that the highest removal efficiency under optimal conditions (pH 7, diazinon concentration of 10 mg/l, and 0.1% nanoparticles) was 83.7%. The modified ENM with proper mechanical properties and porosity, and high flux can be applied as an effective and environment-friendly material to remove diazinon from aqueous solutions.

The contamination of the aquatic environment with emerging micro-pollutants is a serious global concern. The aim of this investigation was to synthesize novel functionalized material (BNAPTES) precursor to natural bentonite in a single pot facile synthetic route. The material was utilized for efficient and selective removal of tetracycline (TC) and triclosan (TCS) in aqueous wastes. The grafting of silane was confirmed with the FT-IR (Fourier Transform Infra-Red) analysis and the EDX (Energy Dispersive X-ray) analysis showed the incorporation of amino group with the bentonite. The structural changes of clay due to silane grafting were studied with the help of XRD (X-ray Diffraction) and BET (Brunner-Emmett-Teller) surface area analyses. Batch adsorption studies showed that functionalized clay significantly increased the selectivity and adsorption capacity of bentonite for TC and TCS. The Langmuir monolayer adsorption capacity was found to be 15.36 and 17.15 mg/g for TC and TCS, respectively. The rapid uptake of TC and TCS by functionalized material followed pseudo-second-rate kinetics. Further, a total of 78% of TC and 73% of TCS were removed within 5 min of contact and the adsorption equilibrium was achieved within 120 min. The influence of background electrolytes and co-existing ions indicated that TC and TCS were selective towards BNAPTES. The loading capacities of the column packed with BNAPTES were found to be 56.00 and 44.42 mg/g for TC and TCS, respectively. Further, BNAPTES was found efficient even in real water treatment since the attenuation of TC and TCS was not affected significantly in the real water matrix.

The present communication addresses the removal of toxic lead, cadmium, and arsenic using iron oxide modified clay-activated carbon composite beads from aqueous solutions. The SEM-EDX analysis was conducted to study the heterogeneity of the surface and the elemental composition of the composite beads. The specific surface area of the composite beads was found to be 433 m2/g. Furthermore, the XRD pattern indicates the intercalation of iron particles between the layers of bentonite clay. The FT-IR analysis suggests that the hydroxyl, carboxyl, and Fe-O were the major functional groups responsible for the removal of lead, cadmium, and arsenic. The Langmuir monolayer sorption capacity of Pb(II), Cd(II) and As(V) were observed to be 74.2, 41.3 and 5.0 mg/g respectively. Kinetic studies indicate that intra-particle diffusion plays a significant role in the removal of these three toxic pollutants. In addition, the composite beads were applied for the adsorption of a ternary mixture of subjected pollutants at low concentrations and found efficient to remove these pollutants up to an acceptable permissible limit of drinking water. The significances of this study propose the potential of composite beads for purifying the water containing toxic pollutants, viz., lead, cadmium, and arsenic.

Batch sorption and leaching of arsenic (1-30mgL-1) on Fe-sericite composite powder and beads were investigated in this study. Fe-sericite composite powder was made from natural sericite modified with iron, and alginate was used to transform the powder into beads. The maximum sorption capacities of the Fe-sericite composite powder (15.04 and 13.21mgg-1 for As(III) and As(V), respectively) were higher than those of the corresponding beads (9.02 and 7.11mgg-1 for As(III) and As(V), respectively) owing to the higher specific surface area of the powder. In addition, the leaching amounts of As(III) from Fe-sericite composite beads (≤ 15.03%) were higher than those of the corresponding powder (≤ 5.71%). However, acute toxicity of As(III)-sorbed Fe-sericite composite beads toward Daphnia magna was not significantly different from that of the corresponding powder (p > 0.05). Considering higher uptake of the powder particles by the daphnids, Fe-sericite composite beads seem to be a more appropriate and safer sorbent for arsenic removal in practical application. Based on Fe content, Fe-sericite composite beads had similar or higher maximum sorption capacities (71.19 and 56.11mgg-1 Fe for As(III) and As(V), respectively) than those of previously reported sorbents.

The aim of this study was to synthesize novel and highly efficient functionalized material (BNMPTS) for selective elimination of Cu2+ and Cd2+ from aqueous waste. The detailed insights of solid/solution interactions were investigated by X-Ray photoelectron spectroscopic analyses. The grafting of silane caused for significant decrease in specific surface area of bentonite from 41.14 to 4.65 m2/g. The functionalized material possessed significantly high sorption capacity (12.59 mg/g for Cu2+ and 13.19 mg/g for Cd2+) and selectivity for these cations. The material showed very high elimination efficiency at a wide range of pH ~2.0 to 7.0 for Cu2+, ~3.0 to 10.0 for Cd2+ and concentration (1.0 to 25.0 mg/L) for Cu2+ and Cd2+. A rapid uptake of these two cations achieved an apparent equilibrium within 60 minutes of contact. The increased level of background electrolyte concentrations (0.0001 to 0.1 mol/L) did not affect the elimination efficiency of these two cations by BNMPTS. Moreover, the common coexisting ions did not inhibit the removal of these toxic ions. Furthermore, high breakthrough volumes i.e., 1.4 and 3.69 L for Cu2+, 2.6 and 6.64 L for Cd2+ was obtained using 0.25 and 0.50 g of BNMPTS respectively in a fixed-bed column operations.

The aim of this study was to obtain indigenously the mesoporous silica (AMS) precursor to 3-aminopropyltriethoxysilane (APTES) and utilizing chitosan a templating natural biopolymer. The textural characteristics of AMS were obtained by the SEM (Scanning Electron Microscopy) and BET (Brunauer–Emmett–Teller) surface area measurements. AMS solid possessed specific surface area of 511.77 m2/g and having pore size and pore volume of 3.38 nm and 0.036 cm3/g, respectively. Further, the AMS was characterized by the XRD (X-ray Diffraction) and FT-IR (Fourier Transform- Infra Red) analyses. The mesoporous silica was employed for efficient removal of cadmium(II) and lead(II) from aqueous solutions. The influence of solution pH, initial cadmium(II)/or lead(II) concentrations, contact time, and background electrolyte concentrations were studied to deduce the mechanism involved at solid/solution interface. The equilibrium state adsorption data were utilized for the Langmuir and Freundlich adsorption isotherms and the Langmuir adsorption isotherm showed a good agreement with the experimental data. Uptake was found to be fairly fast and the kinetic modelling suggested that the adsorption of cadmium(II)/or lead(II) by AMS was occurred through fractal-like pseudo-second order kinetics. An increase in background electrolyte concentrations from 0.0001 to 0.01 mol/L NaNO3 did not affect the removal of lead(II), whereas the cadmium(II) removal was slightly suppressed. The XPS (X-ray Photoelectron Spectroscopy) analysis indicated that removal of cadmium(II) or lead(II) occurred through the formation of a chemical bond with the oxygen atoms present with AMS solid. Furthermore, fixed-bed column adsorption was conducted and the loading capacity of cadmium(II) and lead(II) was found to be 11.54 and 8.59 mg/g, respectively.

The presence of antibiotics in aquatic environments has become a serious concern since they develop the antibiotic/multi-drug-resistant bacteria which further affect to living beings. The study intended to assess the freshly synthesized ferrate (VI) in the degradation of an important emerging micro-pollutant i.e., sulfamethazine (SMZ). Moreover, the real matrix implications are extensively conducted for implication of ferrate (VI) technology as safer and viable options. Batch reactor studies enabled the molar ratio of ferrate (VI) to sulfamethazine is 2:1 with overall rate constant 6,128 mM-2.min-1. Percentage elimination of sulfamethazine was observed Ca. 80% at initial sulfamethazine concentration 0.02 mM and ferrate (VI) dose 0.1 mM. Presence of several co-ions NaCl, Na2HPO4, NaNO3, oxalic acid and NaNO2 showed insignificant effect on elimination of sulfamethazine; whereas the efficiency of ferrate (VI) was lowered due to glycine and EDTA. Mineralization of sulfamethazine is significantly increased at lower pH value (pH 5.0). Further, the removal of sulfamethazine in the real water matrix showed that the elimination efficiency of sulfamethazine is almost unaffected as compared to the distilled water treatment. This implied that ferrate (VI) is a viable and greener option for treatment of emerging water pollutants to enhance the efficiency of existing wastewater treatment plants.

Sericite powder was used as a substrate to immobilize the iron-oxide particles and it was encapsulated into beads using Na-alginate and Fe(III) ions by a simple cross-linking method to obtain iron-oxide modified sericite alginate beads (IMSA). The presence of iron oxide particle and other functional groups of alginate allows interaction of anionic arsenic species as well as the cationic Pb(II) ions with the IMSA beads; therefore, the material possess enhanced affinity towards these two highly toxic pollutants. The surface morphology and chemical composition of the beads were characterized by SEM-EDX analysis. Various functional groups present in the beads were identified by FT-IR analysis. Moreover, the iron content in the beads was obtained by US EPA 3050B method and the stability of immobilized iron was evaluated as a function of pH. The batch experiment showed that an increase in solution pH facilitate the uptake of Pb(II) whereas the As(V) removal found to decrease at higher pH. The simultaneous adsorption study showed that the As(V) removal was significantly high even at basic solution, which is perhaps, due to the presence of Pb(OH)2 precipitates. The adsorption capacity of IMSA beads is evaluated using Langmuir adsorption isotherm and found to be 21.61 mg/g and 133.73 for As(V) and Pb(II), respectively. The adsorption kinetic data of As(V) fit well to pseudo second order kinetic model whereas Pb(II) showed a better fit to the pseudo first order kinetic model. Moreover, 100 times increase in the ionic strength of the solution did not show significant effect in the uptake of As(V) whereas Pb(II) removal was slightly suppressed. This study demonstrates that IMSA beads obtained by exploiting natural sericite, iron oxide and alginate are efficient and sustainable adsorbent for the removal of arsenic and lead from the aquatic environment.

Natural sericite clay was modified with iron-oxide and then the modified sericite was encapsulated into beads by employing the ionic gelation method to obtain Fe-sericite composite beads. The materials were fully characterized by N2 adsorption–desorption isotherm, SEM-EDX, XRD, FT-IR and XPS analyses. Batch experiments showed that the composite beads showed a high uptake of As(V) and phosphate within a wide range of pH and the maximum sorption capacity determined by Langmuir isotherm were found to be 5.780 and 4.446 mg/g for As(V) and phosphate, respectively. The sorption kinetic data indicate that at least 12 h of contact time is necessary to attain the sorption equilibrium and intra-particle diffusion plays a significant role in the sorption process. The presence of background electrolyte (NaNO3) or other heavy metals ions could not significantly affect the uptake of As(V)/phosphate by Fe-sericite composite beads. Furthermore, a fixed-bed column experiment has demonstrated that Fe-sericite composite beads could remove As(V) and phosphate up to acceptable level with a high breakthrough volume even under dynamic conditions. XPS analysis results indicate the successful sorption of As(V)/phosphate and it is assumed that these two pollutants formed an inner sphere complexes with iron oxide present in the composite beads.

Iron oxide nanoparticles were impregnated with the Chlorella vulgaris (CV) microalgae in order to obtain the magnetic biomaterial (magnetic-CV). The materials were characterized by SEM-EDX, HR-TEM, FT-IR and XPS analyses. Further, the magnetic-CV was successfully employed in the removal of Cd(II) and Pb(II) from aqueous solutions. High percentage uptakes of these two toxic ions were observed in a wide range of pH and initial sorbate concentrations. The material was found to be efficient in the rapid uptake of Cd(II)/Pb(II) from aqueous solutions. The increases in background electrolyte concentrations (i.e., 0.001−0.1 mol/L NaNO3) affected the uptake of Cd(II) to a greater extent whereas Pb(II) removal was almost unaffected. This implied that Cd(II) was sorbed with weaker forces whereas the Pb(II) ions were aggregated specifically onto the solid surface forming an inner sphere complexes. Moreover, a simultaneous sorption study inferred that Cd(II) and Pb(II) were sorbed at the different binding sites available at the hybrid biomaterial. Furthermore, the sorption mechanism discussed with FT-IR and XPS analyses has shown that Cd(II) bound with weak electrostatic forces to the dissociated carboxyl or hydroxyl groups available onto the solid surface whereas Pb(II) ions were chemically bound with the amino group of magnetic-CV.

The separation of fine spent sorbents from treated water after remediation is a major difficulty associated with phosphate wastewater treatment technology. In this study, a novel aluminium-pillared acid activated bentonite powder (Al-ABn) and alginate immobilized aluminium-pillared acid activated bentonite beads (Al-ABn-AB) were synthesized and used for the removal of aqueous phosphate. The phosphate removal behaviour of adsorbents were evaluated by batch experiments as a function of various parameters such as pH, initial concentration, contact time, temperature, adsorbent dose and presence of coexisting ions. The sorption isotherm studies by Langmuir model showed 12.87 and 11.11 mgP/g maximum phosphate uptake capacity for Al-ABn and Al-ABn-AB, respectively. The kinetic studies confirm that the adsorption of phosphate by Al-ABn and Al-ABn-AB follows a pseudo-second-order model. The feasibility of Al-ABn-AB was also assessed in continuous mode in fixed bed column and the loading capacity obtained was 4.55 mg/g. The adsorption capacity of Al-ABn-AB beads remained at relatively high even after four regeneration cycles. Furthermore, the applicability of the synthesized adsorbents towards real municipal wastewater confirmed that novel synthesized Al-ABn and Al-ABn-AB are the promising adsorbents for the removal of phosphate from contaminated water.

The aim of this study is to synthesize the three different hybrid materials precursor to natural biopolymer chitosan. The silanes viz., 3-mercaptopropyl trimethoxysilane, trimethoxy(octyl) silane and 3-aminopropyl triethoxysilane were grafted with the chitosan network and were named as CHMS, CHTS and CHAS, respectively. The materials were characterized by the FT-IR spectrometry, SEM–EDX and XPS analyses. These solids were then employed in the efficient removal of Cr(VI) from aqueous solutions using batch and column reactor operations. The functionalized biomaterials possessed extremely high percent removal of Cr(VI) compared to bare chitosan at wide pH range i.e., pH ∼3.0 to 8.0. A fast uptake of Cr(VI) was occurred and high percentage removal was obtained at wide range of Cr(VI) initial concentrations (7.7–100.58 mg/L). The equilibrium state sorption data were utilized for the Langmuir and Freundlich adsorption isotherm studies. Similarly, an increase in background electrolyte concentrations from 0.0001 to 0.05 mol/L NaNO 3 was assessed for the uptake of Cr(VI) by these hybrid materials. Relatively a fast uptake of Cr(VI) by these hybrid materials were obtained and further the time dependence data were fitted well to the pseudo-second-order and fractal-like pseudo-second-order kinetic models rather a pseudo-first-order kinetic model. Furthermore, a detailed sorption mechanism was included with the help of FT-IR, TOC and XPS analyses. In addition, CHMS and CHTS were used for dynamic studies under column reactor operations. The breakthrough curves were then used for the non-linear fitting of the Thomas equation and the loading capacity of the column for Cr(VI) were estimated.

Chitosan is grafted with 3-aminopropyltriethoxysilane under inert atmosphere in acetic acid–ethanol solvent mixture. The materials are characterized by the SEM-EDX and FT-IR analyses. The successful grafting of silane with chitosan is confirmed by the EDX and FT-IR analytical data. The hybrid material is then employed in the remediation of aqueous solutions contaminated with As(V) under batch and column reactor operations. The sorption capacity of chitosan is tremendously increased with the incorporation of 3-aminopropyltriethoxysilane and the hybrid material showed high percent removal of As(V) within the pH ranges between pH 3.0–7.0. The equilibrium sorption is achieved within 120 min of contact and the kinetic data is best fitted to the pseudo first order kinetic model. Moreover, high percentage removal of As(V) is observed in a wide concentration range and the concentration dependence data fitted well to the Freundlich adsorption isotherm. On increasing the background electrolyte (NaNO3) concentration by 100 times decreased significantly the removal of As(V); however, the presence of co-existing ions could not significantly affect the removal of As(V) using the synthesized hybrid material. Furthermore, the loading capacity of As(V) under the dynamic conditions using hybrid material packed column is estimated and found to be 2.576 mg/g.

In this study, the effects of acid activation with high bentonite contents under mild synthetic conditions on textural and structural properties were explored. The alteration features after activation were fully characterized with the help of X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area, Barrett–Joyner–Halenda (BJH) pore size and volume analyses. The active sites were examined using volumetric titration and confirmed with a pyridine adsorbed FT-IR study. The activated bentonite (ABn) was further utilized for the removal of Cu(II) and Pb(II) ions from aqueous solutions. Batch reactor studies showed that the removal of these toxic metal ions was favored by increases in the pH, initial metal concentrations, contact time, and dose of the adsorbents. The equilibrium data obtained at various initial concentrations reasonably fit well with the Langmuir and Freundlich adsorption isotherms. The adsorption process was fast and the kinetic data fit better to the pseudo-second order kinetic model. The presence of other heavy metal ions, such as Cd(II), Fe(II), and Mn(II), did not significantly suppress the removal of both the Cu(II) and Pb(II); whereas the other cations, such as Na+, K+, Ca2+, and Mg2+ caused a notable decrease in the Pb(II) removal. In addition, the breakthrough data obtained in the column studies fit well with the non-linear Thomas equation, and high loading capacities of Cu(II) and Pb(II) were obtained. Therefore, we demonstrated in this study that the low cost ‘ABn’ solid can be employed as a potential adsorbent for the effective treatment of aqueous waste contaminated with Cu(II) and Pb(II).

The present communication addresses the development of a novel hybrid material precursor to natural sericite. The hybrid material is then successfully utilized for efficient removal of cadmium and phenol from aqueous solutions. Initially, sericite was annealed and activated with hydrochloric acid. The activation caused a significant increase in specific surface area of sericite, thereby provided a suitable surface structure for grafting of organosilanes. The activated sericite (AS) was functionalized with 3-aminopropyltriethoxysilane (APTES), and the resultant AS-APTES along with pristine sericite and AS were characterized using SEM–EDX, BET, XRD and FT-IR analyses. Batch reactor studies showed that increase in sorptive pH, contact time, initial concentration and temperature significantly favored the sorption of Cd(II), and a 100-fold increase in background electrolyte concentration did not significantly affect the uptake of Cd(II) or phenol from aqueous solutions. Cd(II) removal was found to be spontaneous and the uptake process was endothermic in nature. Further, the intra-particle diffusion was found to be the rate-limiting step in the sorption of Cd(II). Various physico-chemical parametric studies enabled to discuss the sorption mechanism of these contaminants at the solid/solution interface. In a single pollutant sorption studies, it was deduced that the Cd(II) was forming an inner-sphere complexes, whereas phenol was sorbed through the hydrogen bonding with the amino groups or partitioned within the interspace region. Simultaneous sorption studies suggested that these two pollutants were possibly removed simultaneously by the prevailing hydrophilic and hydrophobic groups. Furthermore, desorption and reusability studies as well as the applicability of the material for real wastewater treatment demonstrated that AS-APTES is a promising solid material for the efficient removal of two important water pollutants i.e., Cd(II) and phenol from aqueous waste.