Adsorption Of Cr Research Articles

Effective Uptake of Cadmium and Chromium from Wastewater Using Carbon-Based Capsicum annuum

Toxic metal ions such as cadmium-Cd(II) and chromium-Cr(VI) are toxic, do not degrade easily in nature, and can cause various disorders and diseases in humans. Removing and monitoring Cd(II) and Cr(VI) ions is necessary for improving water quality. This study aimed to produce an adsorbent from activated carbon of Capsicum annuum and assess its ability to adsorb Cd(II) and Cr(VI) ions from water. The results showed that the adsorbent from C. annuum was porous after its conversion to activated carbon. The pH(PZC) of carbon-based Capsicum annuum was acidic, with a pH of 2.68. The highest capacities for both metal ions were observed at a pH of 1 for Cr(VI) and pH 5 for Cd(II), with capacities of 18.38 and 29.48 mg/g, respectively. The Freundlich sorption model proved to be the most suitable method. The adsorption of Cr(VI) and Cd(II) increased when the initial concentrations were raised from 20 and 60 mg/L; thereafter, a decrease was observed. The data showed that the adsorption of Cd(II) was fast and reached a maximum in 40 min, while Cr(VI) increased with time up to 30 min; thereafter, the rate for Cr(VI) decreased, while equilibrium was reached for Cd(II) ions. The temperature effect showed that the adsorption of Cd(II) and Cr(VI) ions reached a maximum at 55 and 45 °C, respectively. The results of enthalpy change (ΔH°) showed that the uptake process was exothermic, while the change in thermodynamic values of Gibbs energy (ΔG°) indicated that the sorption process was spontaneous and achievable. The greatest adsorption capacities for Cd(II) and Cr(VI) ions were 34.34 and 15.24 mg/g, respectively. The activated carbon from C. annuum proved to be effective for the adsorption of Cd(II) and Cr(VI) from wastewater.

Chromium(VI) and Nitrate Removal from Groundwater Using Biochar-Assisted Zero Valent Iron Autotrophic Bioreduction: Enhancing Electron Transfer Efficiency and Reducing EPS Accumulation.

Current strategies primarily utilize heterotrophic or mixotrophic bioreduction for the simultaneous removal of Cr(VI) and NO3- from groundwater. However, given the oligotrophic nature of groundwater, autotrophic bioreduction could be more appropriate, though it remains notably underdeveloped. Here, an autotrophic bioreduction technology utilizing biochar (BC)-assisted zero valent iron (ZVI) is proposed. The pyrolysis temperature of BC was optimized to enhance electron transfer efficiency and reduce extracellular polymeric substances (EPS) accumulation. BC500, with the superior electron transfer capabilities, was the most effective. After an 11-week period, the ZVI+BC500 biotic column still achieved 100% removal efficiency for Cr(VI) and 93.37±0.33% for NO3-, with initial concentrations of 26 mg/L and 50 mg/L, respectively. Its performance significantly surpasses that of ZVI alone, effectively reducing the interference of Cr(VI) on denitrification. The presence of quinone and phenolic compounds in BC500, serving as electron-accepting and electron-donating groups, improves the efficiency of electron transfer between ZVI and microbes. Metagenomic analysis showed an increase in the growth of autotrophic bacteria such as Hydrogenophaga spp. and Rhodanobacter denitrificans, and heterotrophic bacteria including Arenimonas daejeonensis and Chryseobacterium shandongense. The promotion facilitates the expression of genes associated with Cr(VI) reduction (chrR, nemA) and denitrification (narG, nirS). BC500 also enhanced EPS production, which facilitates the adsorption and reduction of Cr(VI), mitigating its inhibitory effects on denitrification. Notably, in the ZVI+BC500 biotic column, the accumulated EPS primarily consists of loosely bound EPS rather than tightly bound EPS, potentially reducing the risk of pore clogging during in-situ groundwater treatment.

Preparation of MIL-53(Cr) and MIL-101(Cr)/reduced graphene oxide/polyaniline composites for Cr(VI) adsorption

Preparation of MIL-53(Cr) and MIL-101(Cr)/reduced graphene oxide/polyaniline composites for Cr(VI) adsorption

Effective adsorption of Cr(VI) from aqueous solution by Mg-Fe LDH supported on orange peel activated carbon: isotherm, kinetic, thermodynamics and mechanism studies

The toxic Cr(VI) contaminating water released from the metallurgical, dyeing, and electroplating industries is getting worse day by day and is extremely hazardous to human health. Thus, the development of a cost-effective, quick, and efficient adsorbent is highly essential for the Cr(VI) decontamination from wastewater. Herein, a microwave-assisted carbon-based composite called Mg-Fe LDH@OPAC was prepared by assembling Mg-Fe LDH onto orange peel-activated carbon (OAPC). Prior to investigating deeply into the adsorption behavior of the composite, the Mg-Fe LDH@OPAC formation was confirmed by using instrumental techniques like FESEM, EDS, Zeta potential, XRD, FTIR, Raman, XPS, and BET analyzer. The material had a high surface area of 143.9 m2/g and showed a good monolayer Langmuir uptake capacity of 118.36 mg/g. Under ideal circumstances, the maximum amount of Cr(VI) was removed within just 120 min and showed high efficiency in the presence of other coexisting anions respectively. The adsorption was accounted by pseudo-second-order kinetics and spontaneous in nature. Ultimately, a possible adsorption mechanism was suggested, confirmed by XPS studies; which showed that oxidation-reduction, electrostatic interaction, and surface complexation reaction were responsible for Cr(VI) adsorption on Mg-Fe LDH@OPAC surface.

Magnetic activated carbonaceous materials from sugarcane bagasse: Preparation, characterization, and hexavalent chromium removal

The presence of hexavalent chromium (Cr (VI)) in effluents remains a global concern due to its toxic properties. Even though adsorption has been employed for its removal from water, developing sustainable materials with higher adsorption capacities is still pivotal to tackling such contamination. In this study, two magnetic carbons (MC) were produced by hydrothermal carbonization (HTC) of sugarcane bagasse in the presence of iron (III) nitrate at 230 and 270 °C. Both MCs were thermochemically activated at 500 and 700 °C using KOH (1:2; w:w). The materials were characterized in terms of composition, structure, morphology, texture, and surface properties and then evaluated in adsorption studies of Cr (VI). After HTC, some iron phases such as α-Fe2O3, γ-Fe2O3, and Fe3O4 were observed, while thermochemical activation additionally revealed Fe0 and Fe4[Fe(CN)6]3. Activation increased the amount of meso- and macropores, specific surface area, pHzpc, surface hydrophilicity, and carbon and nitrogen contents. The adsorption kinetics study indicated that the pseudo-second-order model describes better the behavior of the materials. The investigation of adsorbent dose showed that doses below 1.00 g L−1 were more efficient in Cr (VI) removal. MC-230 and MC-270 thermochemically activated at 700 °C exhibited the highest Cr (VI) adsorption capacities (10.5 and 15.5 mg g−1, respectively). Therefore, the improved adsorption capacity for Cr (VI) of the materials thermochemically activated at 700 °C was mainly due to their enhanced textural properties.

Effective adsorptive removal of heavy metal anion Cr(Ⅵ) and dye cation methylene blue by the novel 2D material TiVCTx MXene

With the increasingly serious industrial pollution, the effective removal of heavy metal ions and organic pollutants from wastewater has become a key issue of environmental protection. In this paper, a new MXene material, TiVCTx, was prepared by in situ etching, and its adsorption capacity of heavy metal anion Cr(Ⅵ) and methylene blue (MB) dye cation was studied. The effect of adsorption time, pH values, temperatures, initial concentrations of adsorbent and adsorbate, interfering ions on the Cr(Ⅵ) and MB adsorption of TiVCTx was systematically investigated. It is found that TiVCTx has excellent Cr(Ⅵ) and MB adsorption property, the adsorption capacity can be as high as 600mg/g and 1430mg/g, respectively. The adsorption experiments revealed that the adsorption process of Cr(Ⅵ) conformed to the Langmuir isotherm model and the Pseudo-second-order kinetic model, which indicated that the Cr(Ⅵ) adsorption was a heat-absorbing monolayer chemisorption. In contrast, the adsorption process of MB is in accordance with the Freundlich isotherm model and the Pseudo-second-order kinetic model, suggesting that the MB adsorption was an exothermic multilayer chemisorption. The results of X-ray electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis further confirmed that the reductive adsorption and electrostatic adsorption can account for the outstanding Cr(VI) and MB adsorption capacity of TiVCTx, respectively.

Removal of Cr (VI) by crosslinked chitosan adsorbent prepared using simulated copper-containing wastewater

A chitosan (CS) hydrogel bead cross-linked by Cu2+ with a macroscopic spheral shape (designated as CS-Cu-B) was synthesized using simulated copper-containing wastewater without additional crosslinking agents. The optimal conditions for CS-Cu-B formation were identified as 1500 mg/L of Cu2+ concentration, pH 5.4 and 50 °C under which CS-Cu-B was further utilized as an adsorbent for Cr(VI). The adjacent chitosan chains were crosslinked by coordination between positive-charged Cu2+ ions and the amino and hydroxyl groups of chitosan. This enhanced the surface charge and increased the specific surface area of CS-Cu-B, thereby augmenting its Cr(VI) adsorption capacity. The effect of adsorbent dosage, pH of Cr(VI) solution, and presence of coexisting ions on Cr(VI) adsorption was investigated. Detailed analyses of the adsorption kinetics, isotherms and thermodynamics of Cr(VI) on CS-Cu-B were also conducted. CS-Cu-B demonstrated a maximum Cr(VI) adsorption capacity of 90.76 mg/g at pH 4.0 and exhibited excellent reusability, retaining 87.90 % of its adsorption capacity after five adsorption-desorption cycles. Both experimental characterizations and DFT calculation elucidated that the electrostatic attraction adsorption is the main driving force for the adsorption of CS-Cu-B on Cr(VI). A consecutive preparation-adsorption strategy using simulated copper-electroplating wastewater was proposed to facilitate the recycling of heavy metals.

Immobilized chitosan as an efficient adsorbent for columnar adsorption of Cr (VI) from aqueous solution

The current effort focuses on creating an effective adsorbent for Cr (VI) adsorption due to the growing need to address Cr (VI) pollution in aqueous solutions. Chitosan, a biopolymer and polysaccharide with several functional sites, is immobilized on alginate using the ion exchange technique. Both prior to and following Cr (VI) adsorption, the material's shape, crystallinity, and functional groups are reported. Immobilized chitosan was employed to adsorb Cr (VI) in a fixed bed column with variable operational parameters (flow rate, initial chromium content, and bed height). The analysis of breakthrough curves showed that at a flow rate of 10 mL/min, Cr (VI) concentration of 50 mg/L and a bed height of 18 cm, a maximum adsorption of 78.41 % was achieved. The adsorption system and the breakthrough curves were thoroughly understood by using Thomas, Yoon-Nelson and Adams-Bohart kinetic models. There is promise for the large-scale use of synthesized immobilized chitosan because the current adsorption process fits the Thomas and Yoon-Nelson model well and confirms the homogenous bed, low mass transfer resistance, and constant operating conditions throughout the experiment. Furthermore, an exploration of the adsorption mechanism is undertaken and the outcomes are compared with existing literature. The regeneration and reuse tests up to four cycles provided insight into the immobilized chitosan's stability, dependability, and potential for scaling up.

Dual-functional flexible cationic porphyrin-based covalent organic frameworks for selective adsorption and sensitive detection of Cr (VI)

Dual-functional flexible cationic porphyrin-based covalent organic frameworks for selective adsorption and sensitive detection of Cr (VI)

A solar thermoelectric system by temperature difference for efficient removal of chromium (VI) in water and soil

In this work, we designed and developed a facile solar thermoelectric generator (STEG)-based system and a new electrokinetic remediation (EKR) system, which consists of main electrodes and unenergized auxiliary electrodes. The prepared nanocomposite was investigated for the effectiveness of the STEG+PANI-CNT/GF system in remediating Cr-contaminated. Photothermal performance test were applied in order to examine this STEG could export a power density of 365.56mW/dm2 and output potential of 801mV at the temperature difference of 50 ℃. Thus the STEG could be used as the power to construct a Cr(VI) removal system using polyaniline (PANI) film/carbon nanotubes (CNT) modified graphite felt (GF) electrode (PANI-CNT/GF) as cathode and graphite rod as anode. The as-prepared STEG+PANI-CNT/GF system exhibited a significant Cr(VI) removal efficiency (96.2% in water) through electromigration, electro-adsorption and electroreduction. Moreover, a multi auxiliary electrodes (AEs) system (STEG+PANI-CNT/GF+AEs) with six PANI-CNT/GF auxiliary electrodes was constructed in remediating Cr(VI)-contaminated soil, showing Cr(VI) removal efficiency of 16.7-60.1% higher than that of STEG+PANI-CNT/GF. The PANI-CNT/GF auxiliary electrodes could bind Cr(VI) and adjust electric field distribution, contributing to adsorption and reduction of Cr(VI). Consequently, this work provides a promoting approach for heavy metals removal in future application.

Redox active metallene anchored amino-functionalized cellulose composite for electrochemical capture and conversion of chromium

Considering the ubiquity and high toxicity of Cr(VI) species for destroying a sustainable environment, developing energy-efficient method for capturing and detoxifying chromium [Cr(VI) → Cr(III)] is imperative. Herein, ferrocene (Fc) was combined with carboxymethyl cellulose (CMC) and polyethyleneimine (PEI) for Cr(VI) remediation. Fc species possessed reversible redox behavior and low ionization potential, yet it faced challenges with conductivity and stability. Results revealed that, PEI facilitated the binding of Fc within the CMC through electrostatic interactions or coordination bonds, ensuring the good dispersion and stability of Fc. When applied in the electrochemical adsorption of Cr(VI), the combination created a synergistic effect. The presence of Fc and PEI boosted the electrochemical performance by providing faster electronic and ionic transportation, higher specific capacitance coupled with improved electrode-electrolyte interactions, leading to a higher Cr(VI) adsorption capacity over CMC/PEI/Fc (280.5 mg/g) compared to those over CMC and CMC/PEI. The interactions between the Cr(VI) and electrode included the electrosorption, electrostatic interaction of protonated PEI and oxidized Fc species. When the electric field was reversed, the Cr(VI) was electrostatic repulsed and electrocatalytic reduced to Cr(III) with a reduction rate of 85.4 %. This work promoted the development of effective electrosorption materials suitable for complete Cr(VI) removal and detoxification.

Modular hydrogel selectively adsorbs phosphates and hexavalent chromium while enabling phosphate recovery

Electroplating wastewater containing high concentrations of phosphates and hexavalent chromium Cr(VI) poses serious environmental pollution. Moreover, phosphorus, as a non-renewable resource, necessitates its recovery to meet sustainable development goals. To address this issue, this study used sodium alginate as the scaffold module, synthesized lanthanum carbonate in situ within a chitosan module to serve as the phosphate adsorption module, and employed polyethyleneimine (PEI) modules to enhance the adsorption capacity for Cr(VI), successfully fabricating a modular hydrogel (LC-CSP). LC-CSP exhibits a complex porous structure and surface morphology, forming an ultra-low-density fiber network with good strength and elasticity, ensuring uniform distribution and exposure of active sites. Under optimal conditions for single-component adsorption, LC-CSP achieved adsorption capacities of 232.02 mg/g for phosphates and 474.61 mg/g for Cr(VI). Additionally, LC-CSP demonstrated excellent reusability, retaining over 83 % of its performance after five cycles. In simulated electroplating wastewater experiments with various interfering substances, LC-CSP maintained high removal efficiencies (>90.72 %) for phosphates and Cr(VI). Post-experiment, enriched water after phosphate desorption was further treated to recover phosphorus resources in complex water environments. Multiple characterization techniques elucidated the adsorption mechanisms of LC-CSP: phosphate adsorption primarily involved ligand exchange, electrostatic interactions, and hydrogen bonding, while Cr(VI) adsorption included electrostatic interactions, hydrogen bonding, and reduction reactions. Finally, fixed-bed simulated wastewater adsorption experiments validated the technical potential of LC-CSP for practical electroplating wastewater management.

Preparation of Poly(allylamine Hydrochloride) Grafted Porous Boron Nitride Fibers for Efficient Cr(VI) Adsorption from Aqueous Solution.

Cr(VI) pollution poses great harm to the cyclic utilization of groundwater and surface water resources. Efficient adsorbent materials have great potential to change this situation and assist in the restoration of ecosystems. This work chooses porous boron nitride fibers (pBN) with stable physical and chemical properties as the matrix, 3-aminopropyltriethoxysilane (APTES) as the coupling agent, and uses a one-step crosslinking method to graft poly(allylamine hydrochloride) (PAH) onto pBN, forming pBN-AS@PAH with fascinating Cr(VI) adsorption capacity. PAH is uniformly covered and modified on the surface of pBN, and the composite with high specific surface area (383.33 m2/g), large pore volume (0.37 cm3/g), and abundant amino groups. Its equilibrium adsorption capacity for Cr(VI) can reach up to 123.32 mg/g, and the adsorption behavior follows the quasi second-order kinetic model and Langmuir model, indicating the chemical adsorption process of monolayer. The adsorption style belongs to a spontaneous exothermic process and has the optimal adsorption effect at a pH of ~2. Additionally, after cycling for 5 times, the decrease rate of adsorption capacity is less than 10 %, showing an excellent reusability.

Performance and Mechanism of Porous Carbons Derived from Biomass as Adsorbent for Removal of Cr(VI)

To solve the problem of heavy metal hexavalent chromium (Cr(VI)) pollution in water bodies, this study was carried out to prepare nitrogen-doped porous carbon by using bamboo shoots as the raw material and KHCO3 as the activator, which has a good ability to remove Cr(VI) from water bodies. The prepared N-doped carbon materials were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and scanning electron microscopy (SEM). The results showed that the prepared carbon material had hierarchical pore structures and abundant functional groups, which is conducive to the adsorption of Cr(VI). The effects of various factors on the adsorption performance of Cr(VI), such as the carbon materials prepared under different conditions, the pH of the initial solution, the concentration of the initial solution, and the contact time between the carbon and Cr(VI), were explored. The results showed that the bamboo shoot-based nitrogen-doped carbon materials, especially BSNC-800 (prepared at 800 °C with a mass ratio of KHCO3 to bamboo shoot of 4:1), performed well in removing Cr(VI) from a water solution. The maximum adsorption of Cr(VI) by BSNC-800 under equilibrium conditions was 385.8 mg g−1 (conditions: at the pH of 2 with the initial concentration of 400 mg L−1). The adsorption kinetics and isotherms were analyzed, and the adsorption mechanism was discussed. It can be found that the adsorption of Cr(VI) by BSNC-800 fits better with the Langmuir isotherm model and the pseudo-second-order kinetic model. The adsorption mechanism between the Cr(VI)-containing solution and BSNC-800 was controlled by membrane diffusion and chemisorption. The results broaden the ways of utilizing biomass resources as precursors of carbon materials, which is significant and helpful for applying biomass carbon materials as adsorbents for wastewater treatment.

ENVIRONMENTAL ASPECTS OF WASTE-DERIVED BOTTOM BLEND CLAY LINERS INCORPORATING ZEOLITE AND BENTONITE

This research investigated the effects of incorporating bentonite and zeolite into bottom blended clay liners (BBCLs) on their engineering properties and adsorption capacity. BBCLs composed of clay, water treatment residue, and calcium carbide in a 40:40:20 ratio by volume were investigated with the addition of 1, 2, and 3 wt.% bentonite or zeolite. The experimental results indicated that bentonite and zeolite had positive effects on the slake durability index and the equilibrium time for the adsorption of lead (Pb) and chromium (Cr) from the leachate, whereas the unconfined compressive strength (UCS) and coefficient of permeability were negatively affected compared to those of the samples without bentonite and zeolite. At 56 days, the UCS of BBCLs with bentonite and zeolite decreased from 3.4 to 2.2MPa, while the coefficient of permeability of all the samples met the regulatory limit of sanitary landfills, which was given at 1×10-7cm/s. The slake durability index of all samples was lower 50% but it remained higher compared to BBCLs without bentonite and zeolite (approximately doubled). Both additives enhanced the equilibrium time and percentage of Pb and Cr adsorption by about 20% and 200%, respectively. SEM-EDS results show the adsorption of Pb and Cr onto the raw materials, calcium silicate hydrate (CSH), zeolite, and bentonite. Therefore, the addition of zeolite can increase the ability to adsorb heavy metals form leachate, which is suitable for use in secured landfills.

Adsorption of Cr(VI) and phosphate anions by amino-functionalized palm oil fibers.

This work developed a novel sustainable adsorbent (PF-Aq) prepared by the amino-functionalization of palm oil fibers (PF). XPS, SEM/EDS, TGA/DSC, and FT-IR techniques proved the successful functionalization of the PF with the amino group. The PF-Aq adsorbent presents a high adsorption capacity for phosphate and Cr(VI) ions. Adsorption kinetics of the ions onto the PF-Aq followed the general-order models, with 240- and 300-min equilibrium times for phosphate and Cr(VI), respectively. The Freundlich equilibrium model can explain the adsorption of phosphate and Cr(VI) on the PF-Aq. Besides, the maximum adsorption capacities were 151.07mgg-1 for phosphate and 206.08mgg-1 for Cr(VI). The best pH for the adsorption of both ions on PF-Aq was 4.0. Interestingly, adsorption was exothermic for phosphate and endothermic for Cr(VI). The adsorption capacities were reduced by 16% for phosphate and 10% for Cr(VI) after 5 adsorption-desorption cycles, demonstrating the good recyclability of the PF-Aq. It can be concluded that PF-Aq is a relevant adsorbent to uptake phosphate and Cr(VI) from water due to its high adsorption capacity, low cost, recyclability, availability, and fast kinetics. Finally, the excellent adsorption potential results from inserting amino groups in the PF, allowing electrostatic interactions between adsorbent and adsorbate.

Anthill clay activated Ocimum gratissimum extract for effective adsorption of methylene blue and chromium (VI) ion from wastewater: Insights into the adsorption isotherms, kinetics, thermodynamics, and mechanisms

The removal of methylene blue (MB) dye and hexavalent chromium (Cr(Vl)) ions from water bodies have necessitated the search for a promising adsorbent material with high adsorptive performance, facile operation, and economical. Here, a novel adsorbent was prepared by activating anthill clay (AC) with Ocimum gratissimum leaf extract (OG@AC) by ultrasonic strategy method to eliminate MB and Cr(Vl) from the aqueous environment; however, the activation strategy serves as an important factor that influenced the adsorptive performance towards MB and Cr(Vl). Furthermore, a high BET surface area of 120.48 m2/g was measured for OG@AC which is attributed majorly to the green activation strategy. The SEM micrograph of OG@AC was seen to have displayed a leaf-like plate formed by quartz and kaolin. In the batch experimental study, the MB and Cr(Vl) adsorption capacities towards OG@AC were determined to be 227.52 and 143.45 mg/g, respectively. Also, the adsorption kinetics and isotherms models results revealed that the adsorption process of OG@AC towards MB and Cr(Vl) was best described by pseudo-first-order and Freundlich models, suggesting that the adsorption process involves a multilayer physisorption. Moreso, thermodynamic results revealed the adsorption process is feasible, spontaneous, and endothermic in nature. The OG@AC exhibited an outstanding regeneration ability and stability towards MB and Cr(Vl) by maintaining a removal efficiency of 79.11 % and 81.20 % even at the tenth successive adsorption-desorption cycles. Overall, this research sheds more insight on how anthill clay is activated using a feasible design and green chemical (Ocimum gratissimum leaf extract) to enhance its adsorptive performance towards MB and Cr(Vl), which can broaden its wide application in the real world.

Effect of modifiers on Cr (VI) adsorption performance of activated modified-hydrochars

Hexavalent chromium (Cr (VI)) is high toxic and solubility in aquatic systems, which has attracted severe environment issues. In this work, corn straw, as raw biomass material, was modified by citric acid, ZnCl2, NaOH, or (NH4)2Fe(SO4)2 via hydrothermal carbonization process, and further activated by KOH to obtain the activated modified-hydrochars. The influence of different modifiers on the Cr (VI) adsorption performance for activated modified-hydrochars was investigated by controlling adsorbent dosages, adsorption time and different Cr (VI) concentrations at pH of 3.0 under room temperature. Among these absorbents, the activated modified-hydrochar modified by ZnCl2 possessed the excellent microporous characteristics and a high specific surface area of 1532.904 m2 g-1, thus exhibiting the Cr (VI) removal rate of 99.6wt.%. Cr (VI) was reduced to Cr (III) by -OH of activated modified-hydrochars during the Cr (VI) adsorption experiments. Due to higher R2 (>0.99) by kinetics analysis, pseudo-second-order kinetics was confirmed and further the Cr (VI) removal for the activated modified-hydrochars was a chemical adsorption process. The regression coefficients (R2) of the Langmuir model for all activated modified-hydrochars were higher than those of Freundlich model, which meant that Langmuir monolayer chemisorption was more consistent with the Cr (VI) adsorption process in this work.

Feasibility and mechanism of adsorption and bioreduction of hexavalent chromium using Rhodopseudomonas palustris immobilized on multiple materials

Rhodopseudomonas palustris immobilized on multiple materials was used to invistigate Cr(VI) adsorption and bioreduction. The highest Cr(VI) removal (97.5%) was achieved at 276h under the opitimed conditions of 2.5% SA, 8% PVA, and 50% filling degree. The highest adsorption capacity was obtained at 11.75 mg g−1 under 300 mg L−1 Cr(VI). Results from adsorption kinetics and isotherms indicated that Cr(VI) adsorption of immobilized photosynthetic bacteria (IPSB) was consistent with the Freundich model and the pseudo-second-order kinetic model (qe = 14.00 mg g−1). SEM and FTIR analyses verified that the porous multilayer network structure of IPSB provided more adsorption sites and functional groups for the removal of Cr(VI). Furthermore, the maximum Cr(VI) reduction efficiency of IPSB was achieved at 10.80 mg g−1, which correlated with the up-regulation of chrR gene expressions at 100 mg L−1 Cr(VI). This study demonstrated the dual mechanisms of Cr(VI) removal in IPSB-treated Cr wastewater, involving both chemisorption and bioreduction working synergistically.

Adsorption Performance and Photocatalytic Activity of La-TiO2@kaolin Composites

Abstract La-TiO2@kaolin(LTK) composites were prepared via sol-gel method with kaolin, lanthanum nitrate and tetrabutyl titanate as raw materials. The samples were characterized by XRD, SEM/EDS, and UV-Vis. The visible light photocatalytic reduction activity and adsorption performance of samples for Cr(VI) were studied. The results showed that La doping can refine TiO2 grains, stabilize phase structure of anatase TiO2, and expand its absorption spectrum, thereby enhancing its photocatalytic reduction activity. Due to the composite of kaolin, the dispersion of TiO2 is improves and it is endowed with a large specific surface area lead to enhance its adsorption ability for Cr(VI). The adsorption equilibrium process of LTK for Cr(VI) conforms to the Langmuir equation model. The coupling effect of doping and composite modification improves the adsorption and visible light catalytic reduction activity of Cr(VI) over composite material samples. The adsorption-photocatalytic removal rate of LTK for Cr(VI) under visible light irradiation for 6 hours reached the highest of 96.5%. The apparent first-order kinetic constant of its photocatalytic reduction reaction was 2.6 times that of pure TiO2.