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A novel adsorbent (AC/Fe 3 O 4 @SiO 2 –NH 2 ) was synthesized via a co-condensation process for the enhanced removal of Pb(II) from aqueous solutions. Characterization analyses including SEM, TEM, BET and XRD confirmed the successful integration of magnetic nanoparticles and amino groups with carbon matrix. Results demonstrated that AC/Fe 3 O 4 @SiO 2 –NH 2 (mass ratio of AC to Fe 3 O 4 was 1:0.25) with specific surface area (48.9 m 2 /g) showed higher adsorption capacity for Pb(II) as compared to other mass ratios. Kinetics study revealed that the adsorption reach equilibrium within 20 h and the maximum adsorption capacity of 104.2 mg/g was achieved with increasing the initial concentration from 20 to 250 mg/L using AC/Fe 3 O 4 @SiO 2 –NH 2 . Maximum removal efficiency was recorded at pH 5.2 and the removal capacities toward four divalent metal ions calculated by the Langmuir model were found to be in the order of Pb(II) > Cu(II) > Ni(II) > Cd(II). Furthermore, Δ G 0 decreased from –1.6 to −3.1 kJ/mol with increase in temperature from 293 to 333 K illustrating that the adsorption was spontaneous and an endothermic process. Complexation adsorption mechanism was found prominent in FTIR and XPS analyses between Pb(II) and AC/Fe 3 O 4 @SiO 2 –NH 2 due to the presence of amino groups. [ABSTRACT FROM AUTHOR]

A selective adsorbent for Hg(II) was prepared by coating Fe 3 O 4 nanoparticles with SiO 2 which was further functionalized with thiol (–SH) group. The new adsorbent (Fe 3 O 4 @SiO 2 -SH) was shown to adsorb aqueous Hg(II) species in a wide range of pH (1.0–8.0) conditions. The Hg(II) adsorption capacity q e was more than 90.0 mg g −1 at pH > 3.0, and was slightly decreased to 84.6 mg g −1 under strong acidic conditions due to the electrostatic repulsion. The Langmuir isotherm model fitted the adsorption data better than the Freundlich, Temkin, and Dubinin-Radushkevich isotherms models. The maximum adsorption capacity of Fe 3 O 4 @SiO 2 -SH for Hg(II) was 132.0 mg g −1 . The adsorption kinetics were shown to follow the pseudo-second-order kinetic model, and the kinetic constant k 2 was 2.4 × 10 −3 g mg −1 min −1 . The magnetic retrieve of the newly-developed adsorbent was easily carried out via an external magnetic field, enabling both excellent adsorbent utilization and adsorption efficiency at high Hg(II) concentrations. [ABSTRACT FROM AUTHOR]

Abstract: The adsorptive removal of As(V) from aqueous solutions using iron-coated honeycomb briquette cinder (Fe-HBC) is presented. Low cost mechanical granulation process was integrated with surface amendment technology to prepare iron-oxide modified granular adsorbent for clean water production. Detailed characterizations were performed using FTIR, XRD, EDS and SEM techniques. Operating parameters including initial As(V) concentration, pH, contact time, adsorbent dose, iron leaching and the effects of competing ions on As(V) removal were evaluated. Results demonstrated that high amount of arsenate (961.5μgg−1) was adsorbed at pH 7.5 in 14h contact time. Langmuir, Freundlich and Temkin isotherm models were used to analyze the adsorption data, whereas Langmuir model was found to best represent the data with a correlation co-efficient (R 2 =0.999). Thus, As(V) sorption on Fe-HBC surface suggested monolayer adsorption and indicated surface homogeneity. Moreover, the dimensionless parameter (R L) value calculated to be about 0.118 that reiterated the process is favorable and spontaneous. The influences of competing ions on As(V) removal decreased in the following order: . The profound inhibition effects of revealed a high affinity toward iron(oxy) hydroxide. Life-cycle assessment confirmed that spent HBC is non-hazardous and can be used as a promising sorbent for arsenic removal. [Copyright &y& Elsevier]

This work aimed to develop a feasible technology to reuse dead pig biowaste for heavy metals removal, which was first carbonized into pig bone char (PBC) after pyrolysis and further functionalized with amino (NH 2) to improve its affinity with heavy metals. The application of PBC after NH 2 -functionalization for aqueous heavy metals removal was explored, including Pb2+, Cu2+, and different complex Cu(II) species. PBC@SiO 2 -NH 2 showed comparable performance with AC@SiO 2 -NH 2. The adsorption capacity of Pb2+ and Cu2+ by PBC@SiO 2 -NH 2 was 120 and 30 mg g−1, respectively. The NH 2 functionalization enhanced the adsorption of complex Cu(II) species, and PBC@SiO 2 -NH 2 exhibited good performance under a wide pH range and coexisting ions. The adsorption of Cu(II) EDTA species with an EDTA/Cu(II) molar ratio of 1.0 by PBC would be enhanced ~3 times and ~6 times after NH 2 functionalization and further addition of Fe3+, respectively. The results of EDX, elemental mapping, and XPS confirmed the adsorption of Cu(II) species. The adsorption kinetics, isotherm, and thermodynamics of different Cu(II) species by PBC@SiO 2 -NH 2 were investigated. The regeneration of PBC@SiO 2 -NH 2 was easily performed via acidic wash. These results suggested the application potential of the reuse of biowaste, which could be a promising adsorbent for aqueous heavy metals after specific functionalization. [ABSTRACT FROM AUTHOR]

The ubiquitous heavy metal(loid)s (HMs) contamination has triggered great concern about food safety, while sequestration and separation of trace HMs from herbal extracts still calls for appropriate sorbent materials. In this work, gum acacia was modified by cysteine to form a cysteine-acacia intermolecular complex (Cys-GA complex) via facile mechanochemical synthesis, aiming at capturing multiple HMs simultaneously. Preliminary screening confirms the superiority of Cys-CA complex for both cationic and anionic HMs, and determines an optimum Cys/GA mass ratio of 9:1 to achieve high removal capacities for Pb(II) (938 mg g−1), Cd(II) (834 mg g−1), As(V) (496 mg g−1), and Cr(VI) (647 mg g−1) in simulated aqueous solution. The analysis on HMs-exhausted Cys-GA complex indicates that Pb(II), As(V), and Cr(VI) tend to be removed through chelation, electrostatic attraction, and reduction, while Cd(II) can only be chelated or adsorbed by electrostatic interaction. The batch experiments on commercial herbal (e.g. Panax ginseng , Glycine max , Sophora flavescens , Gardenia jasminoides , Cyclocarya paliurus , and Bamboo leaf) extracts indicate that Cys-GA complex can reduce HMs concentration to attain acceptable level that comply with International Organization for Standardization, with negligible negative effect on its active ingredients. This work provides a practical and convenient strategy to purify HMs-contaminated foods without introducing secondary pollution. [Display omitted] • Cysteine-gum acacia intermolecular complex was fabricated by mechanochemistry. • Cys-GA achieves heavy metal(loid)s sequestration for both cationic/anionic species. • Sequestration mechanism includes chelation, electrostatic attraction, and reduction. • Cys-GA reduces the heavy metal(loid)s in herbal extract to an acceptable level. • Cys-GA triggers negligible negative effect on active ingredient of herbal extract. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 2,4-DCBA was efficiently removed by moveable carbon-supported Pd catalysts. • The catalysts morphologies and chemical structures maintained during the reaction. • Pd/CB exhibited the highest adsorption and dechlorination ability. • The issues of easy loss of Pd and poor long-term performance were addressed. Abstract In the present study, carbon black (CB), multi walled carbon nanotubes (MWCNTs), and granular activated carbon (GAC) were employed to support palladium (Pd) catalyst. The prepared Pd/CB, Pd/MWCNTs and Pd/GAC moveable catalysts were aimed to address the common issues (easy loss of catalyst and poor long-term performance) of normal fixed catalysts. The results of various characterizations (e.g., TEM, XRD, and XPS) clearly show that the Pd nanoparticles were successfully loaded onto the carbon-supports, especially CB and MWCNTs. And more importantly, the morphologies, Pd distribution, and chemical structure of these moveable catalysts were almost not changed after 3 h reaction. The moveable Pd/CB, Pd/MWCNTs, and Pd/GAC catalysts had good reactivity for 2,4-dichlorobenzoic acid (2,4-DCBA) dechlorination, and Pd/CB exhibited the best performance. The Pd/CB also shows the best adsorption capacity of 2,4-DCBA and dechlorination product (benzoic acid, BA), and the adsorption of BA was significantly inhibited in the presence of current due to the repulsion between the both negatively charged compounds and adsorbents. The removal of 2,4-DCBA and the generation rate of BA was improved with a pre-adsorption process, which was a promising strategy with higher dechlorination rate and shortened electrolysis time. Moreover, the loss of Pd catalyst was negligible during the 10 consecutive cycles experiment, and the improved longevity could be expected. These results suggested the good reactivity, stability, and reusability of moveable Pd/CB catalyst. [ABSTRACT FROM AUTHOR]

Iron sulfide (FeS) nanoparticles with large specific surface area and abundant pore structure have been recognized as effective Hg(II) adsorbents. However, bare FeS nanoparticles can aggregate easily, which greatly limited their engineering applications. In this study, FeS nanoparticles were stabilized by biomaterials, including sodium carboxymethyl cellulose (CMC), gelatin and starch, and thoroughly investigated for the stabilization effects. Results demonstrated that the three biomaterial stabilized FeS nanoparticles namely CMC-FeS, gelatin-FeS and starch-FeS enhanced the adsorption efficiency significantly. The maximum adsorption capacities of CMC-FeS, gelatin-FeS and starch-FeS (mass ratio of stabilizer to FeS was 1:6) achieved ∼1726 mg/g, ∼1939 mg/g and ∼1989 mg/g respectively, which were over twice of the bare FeS. TEM images suggested that biomaterial-FeS nanoparticles were dispersed more uniformly than bare FeS. The removal processes of the three materials obeyed pseudo-second-order kinetic model ( R 2  ≥ 0.9986), implying that the rate-limiting step was the chemical sorption process. High removal efficiency of biomaterial-FeS nanoparticles was observed in the initial pH range of 6–11. The presence of Cl − could accelerate the reaction process, whereas the presence of humic acid (HA) could inhibit Hg(II) uptake. In addition, high concentration of coexisting cations (30 mM as Cd 2+ , Pb 2+ , Cu 2+ , and Ca 2+ ) had no significant effect on Hg(II) removal. [ABSTRACT FROM AUTHOR]

Carbon-based nanomaterials, especially carbon nanotubes and graphene, have drawn wide attention in recent years as novel materials for environmental applications. Notably, the functionalized derivatives of carbon nanotubes and graphene with high surface area and adsorption sites are proposed to remove heavy metals via adsorption, addressing the pressing pollution of heavy metal. This critical revies assesses the recent development of various functionalized carbon nanotubes and graphene that are used to remove heavy metals from contaminated water, including the preparation and characterization methods of functionalized carbon nanotubes and graphene, their applications for heavy metal adsorption, effects of water chemistry on the adsorption capacity, and decontamination mechanism. Future research directions have also been proposed with the goal of further improving their adsorption performance, the feasibility of industrial applications, and better simulating adsorption mechanisms. [ABSTRACT FROM AUTHOR]

In this study, reduced graphene oxide (RGO) and different stabilizers (hexadecyltrimethylammonium bromide, starch, and carboxymethyl cellulose) were applied to simultaneously support and stabilize Fe-Mn binary oxide (FeMnO x ) nanohybrids, and enhanced removal of As(III)/(V) from water was achieved. TEM images shows that the aggregation of FeMnO x on RGO was effectively inhibited after the starch stabilization, meanwhile, the loading of FeMnO x on RGO was also increased. The adsorption capacity of As(III) and As(V) on starch-FeMnO x /RGO via Langmuir isotherm model was 78.74 mg g −1 and 55.56 mg g −1 , respectively, which was 1.99 and 2.39 times higher than bare FeMnO x . The adsorption kinetics was well fitted by the pseudo-second-order model. The effects of initial pH and coexisted anions were investigated. Over 90% of As(III) and As(V) could be removed by starch-FeMnO x /RGO during the five consecutive adsorption-desorption cycles. The results revealed the potential of the RGO supported and starch stabilized FeMnO x as an efficient adsorbent for arsenic removal from water. [ABSTRACT FROM AUTHOR]

In this study, SiO 2 -EDTA was prepared by silanization reaction between N-(trimethoxysilylpropyl) ethylenediamine triacetic acid, trisodium salt (EDTA-silane) and hydroxyl groups for enhanced removal of Pb(II), Pb(II)-Cit (the clathrate generated by Pb(II) and trisodium citrate dehydrate(Cit)) and Pb(II)-EDTA(20%) from aqueous solutions. SiO 2 -EDTA composites were characterized using SEM, TEM, EDX-mapping, FTIR, XPS and TGA analyses. The influence of solution pH, initial concentration, contact time and co-existing interferents were also studied. Results demonstrated that the composite successfully adsorbed 147.52, 107.65 and 124.18 mg g −1 of Pb(II), Pb(II)-Cit, and Pb(II)-EDTA (20%), respectively with the initial Pb(II) concentration of 100 mg L −1 . Kinetics study revealed that the adsorption rate was significantly high at the beginning and then reached to equilibrium within 1.0 h. Moreover, Pb(II) adsorption capacities were found to considerably affected by co-existing cations and not inhibited by natural organic matter (NOM). Characterization analyses confirmed that EDTA was successfully assembled on SiO 2 which had been used as a supporting matrix due to its huge specific surface area. Findings from this study suggested that the present composite could be considered as a promising adsorbent for large scale treatment of wastewater containing elevated Pb(II) concentration. [ABSTRACT FROM AUTHOR]

In this study, EDTA-functionalized Fe 3 O 4 (Fe 3 O 4 @SiO 2 -EDTA) was prepared by silanization reaction between N-(trimethoxysilylpropyl) ethylenediamine triacetic acid (EDTA-silane) and hydroxyl groups for Pb(II) and Cu(II) removal from aqueous solutions. Fe 3 O 4 @SiO 2 -EDTA composites were characterized using SEM, TEM, EDX, FTIR, XPS, TGA and saturated magnetization techniques. Maximum Pb(II) adsorption capacity was found to be 114.94 mg g −1 with SiO 2 /EDTA molar ratio of 2.5:1. The adsorption rate was significantly fast and the equilibrium was reached within 10 min. The optimum pH was recorded to be 5.0. The maximum adsorption capacity of the studied heavy metal ions calculated by Langmuir model followed the order: Cu(II) (0.58 mmol g −1 ) > Pb(II) (0.55 mmol g −1 ) ≈ Ni(II) (0.55 mmol g −1 ) > Cd(II) (0.45 mmol g −1 ). Moreover, Pb(II) and Cu(II) adsorption capacities were not significantly affected by co-existing cations and NOM. These results suggested that this adsorbent can be considered as a promising adsorbent to remove Pb(II) and Cu(II) from wastewaters. [ABSTRACT FROM AUTHOR]

Magnetic biochar is increasingly known as a multi-functional material and the appropriate synthesis method further increase its efficient applications. In this study, the effects of synthesis methods on the fabrication of Kans grass straw/biochar (KGS/KGB) with Fe 3+ /Fe 2+ by chemical co-precipitation and subsequently pyrolyzing at 500 °C for 2 and 4 h were studied in details, and compared their As(III, V) adsorption potentials under different operating conditions. Magnetic biochars (MKGB3 and MKGB4) prepared from KGS revealed of superior Fe 3 O 4 loading, higher As(III, V) adsorption efficiency and saturation magnetization (45.7 Am 2 kg −1 ) than that of KGB (MKGB1 and MKGB2). Moreover, Thermogravimetric analysis (TGA) demonstrated three stages of decomposition and the MKGB3 and MKGB4 generated higher residual mass (>60%) at stage 3 (1000 °C) due to greater Fe 3 O 4 composite in biochar matrix and turned to be thermally more stable. As(III) and As(V) adsorption equilibrium data well fitted in Langmuir model and followed the order: MKGB4 > MKGB3 > MKGB2 > MKGB1. The maximum As(III) and As(V) adsorption capacities were about 2.0 mg g −1 and 3.1 mg g −1 , respectively. The data best fitted in pseudo-second-order ( R 2 > 0.99) rather than pseudo-first-order kinetics model indicating of more complex mechanism. The adsorption of As(III) and As(V) was found to decrease with increasing in ionic strength of competing ions and PO 4 3− was found to strongly inhibit arsenic adsorption. Highest desorption was achieved at pH 13.5 using NaOH. This study suggests that selective adsorbent synthesis method could be useful to prepare effective adsorbent for toxic metals immobilization. [ABSTRACT FROM AUTHOR]

Highlights: [•] Arsenic removal performance of SSFs containing HBC and Fe-HBC (50% w/w) is studied. [•] Over 99% and 98% arsenic removals were achieved in SSF(a) and SSF(b) under oxic-environment. [•] Two steps in situ mechanism is proposed to convert As(III) into As(V) and subsequent adsorption. [•] Low levels of influent co-occurring ions did not significantly interfered arsenic removal. [•] Filter with low-cost adsorbents could be proposed as feasible and efficient method for arsenic removal. [ABSTRACT FROM AUTHOR]

Abstract: Water pollution caused by ammonia nitrogen has attracted a great attention as its toxicity affects both the environment and human health. The objective of this paper was to investigate the adsorption behavior of NH4 +-N from aqueous solution by activated carbons prepared from rice husk. The physico-chemical properties of the activated carbon were characterized by Brunauer-Emmett-Teller (BET) test, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was found that the NH4 +-N adsorption on the rice husk derived carbons was dependent on adsorbent dosage and solution pH. The adsorption kinetics and isotherms of NH4 +-N by rice husk carbon were also investigated, and good correlation coefficients were obtained for the pseudo-second order kinetic equation. Dubinin-Radushkevitch (D-R) adsorption isotherm model could better describe the adsorption behavior of NH4 +-N on the rice husk carbon. Calculated by D-R model, the adsorption course of NH4 +-N on the rice husk carbon was favored chemical ion-exchange mechanism. Moreover, the activated carbon adsorbed NH4 +-N was highly fertilizer conservation especially for the nitrogen element. It was proposed that the amount of removed NH4 +-N from aqueous solutions would increase evidently treated by rice husk carbon if combined with biological method. [Copyright &y& Elsevier]

Abstract: Nanoscale Pd/Fe particles were combined with multi-walled carbon nanotubes (MWNTs) to prepare supported particles (MWNT-stabilized Pd/Fe), which were used to remove 2,4-dichlorophenol (2,4-DCP). The adsorption capacity of MWNTs was found to be increased with the increasing amount of chlorine atoms, and the removal rates of phenol (P), 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-DCP reached 19.7%, 60.5%, 72.0% and 95.1% respectively, in 1min by MWNTs due to π–π interaction. The adsorption kinetics and adsorption isotherm were also discussed. MWNTs as a supporter, was effective for avoiding the agglomeration of nZVI. Furthermore, the speedy removal efficiency of the initial substances (2,4-DCP) reached about 50% in 1min, and over the time continued to rise to 100%, remaining low concentrations (<1mgL−1) of the intermediate substances (o-CP, p-CP), and gradual release of the final substance (P) from MWNT-stabilized Pd/Fe composites during the whole process, proposed a novel method for in situ remediation technology. [Copyright &y& Elsevier]

Abstract: Acid treatment is a routine demineralization process to obtain black carbon (BC), but there has been little systematic research about its influence on BC’s characteristics. In this study, elemental analysis, SEM, FTIR, and Boehm titration were used to investigate that effect. Our results showed that the acid treatment had little influence on the sorption of fly ash and soot to pentachlorophenol (PCP), but it greatly increased the sorption of rice chars to PCP. There were two competing effects of acid demineralization on the adsorption capacity of BC. On one hand, it increased the amount of the acidic functional groups, which decreased the adsorption capacity. On the other hand, it increased the surface and pore volume of BC and caused the emergence of hidden carbon enclosed by minerals, which in turn increased the sorptivity significantly. Especially for rice chars (600°C), after acid treatment, their surface area increased from 3.52 to 235m2 g−1 and the sorption capacity coefficient increased from 2.12 to 4.10. [Copyright &y& Elsevier]

Abstract: The adsorption of Cu(II) from aqueous solution by carbons prepared from rice husk through pyrolysis and steam activation was studied. The rice husk carbon was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and its pore structure was also examined. After comparing different characteristics of the carbons prepared under different conditions and their adsorption abilities of Cu(II), the optimum temperature for pyrolysis and steam activation was chosen as 700 and 750°C, respectively, using 3% (V/V) steam as the best activation gas. It was found that the Cu(II) adsorption on the rice husk derived carbons was pH and temperature dependent with an optimum pH value of 5.0, and an equilibrium time of 24h. The adsorption kinetics and isotherms of Cu(II) by the rice husk derived carbons were also investigated under four different temperatures, and good correlation coefficients were obtained for the pseudo-second-order kinetic models, and the Langmuir isotherm model fitted very well with the experimental data. The mean free energy E (kJmol−1) obtained in the Dubinin-Radushkevitch (D-R) adsorption isortherm equation indicated a chemical ion-exchange mechanism. Several thermodynamic parameters were also caculated to predict the nature of adsorption process. [ABSTRACT FROM AUTHOR]

The wide use of antimony in textile industry has posed threat to ecological health and attracted increased attention. The objective of this work was to develop enhanced coagulation strategies including PFS/FeSO 4 and aerated PFS/FeSO 4 for efficient antimony elimination from textile wastewater matrix. With a dosage of 0.75 mM Fe, aerated PFS/FeSO 4 coagulation could achieve 82.6% removal of 500 μg L−1 Sb(V) from simulated textile wastewater, which was better than PFS (77.6%) and PFS/FeSO 4 coagulation (79.9%). Compared with PFS and PFS/FeSO 4 coagulation, aerated PFS/FeSO 4 strategy could meet the indirect discharge standard (<100 μg L−1), without any other additional treatment. pH ranged from 5 to 6 could reach 93.8% Sb(V) removal, by affecting coagulant hydrolysis and charges on flocs. Phosphate ion with a level more than 0.03 mM could compete with Sb(V) species and thus reduced its removal. Temperature of 35 °C could lead to enhanced Sb(V) removal by accelerating coagulant hydrolysis. Flocs of aerated PFS/FeSO 4 had smaller average size than that of PFS and PFS/FeSO 4 coagulation. FeOOH was the hydrolysis product of aerated PFS/FeSO 4 strategy. Adsorption, rather than direct and co-precipitation was predominant in the coagulation mechanism. From the phosphate extraction test, 64% of the Sb could form inner-sphere surface complex during aerated PFS/FeSO 4 coagulation removal. Image 1 • Aerated PFS/FeSO 4 was the optimum strategy for Sb(V) coagulation. • The Sb(V) after aerated PFS/FeSO 4 coagulation was under the discharge standard. • The Sb (V) removal efficiency was significantly affected by pH and phosphate. • Adsorption played an important role in aerated PFS/FeSO 4 coagulation for Sb(V). [ABSTRACT FROM AUTHOR]