Removal Of Hexavalent Chromium Research Articles

Removal of hexavalent chromium from aqueous by Chitosan-stabilized FeS

In this study, FeS and chitosan (CTS) were compounded to form a new Cr (Ⅵ) treatment material FeS/CTS. FeS/CTS was characterized by SEM, FTIR, XRD, XPS, BET, etc, and the removal performance and mechanism of FeS/CTS for Cr (Ⅵ) were also discussed. The removal of Cr (Ⅵ) by the composite was the result of electrostatic force, redox reaction, complexation and precipitation. When the initial concentration of Cr (Ⅵ) was 50 mg∙L−1, the removal of Cr (Ⅵ) was attributed to 87.14% reduction and 12.86% adsorption. The fitting results of the kinetic and isothermal models proved that chemical adsorption playsed a dominant role in the removal process. At pH 5 and the initial Cr (Ⅵ) concentration of 40 mg∙L−1, the removal rate of Cr (Ⅵ) by the composite could reach 99.90%. All results showed that FeS/CTS composite can be used as a potential Cr (Ⅵ) removal material in water.

Enhanced removal of hexavalent chromium from aqueous solution by nano-TiO2 modified zero valent iron under UV light irradiation: Performance, reaction kinetic and the role of iron oxide interfacial layers

The major problem for nano-zero valent iron (nZVI) application is the degradation of performance due to the continuous oxidation during reaction process. A composite has been prepared, which was developed by coating TiO2 nanoparticles onto the surface of nZVI (TiO2@nZVI). A series of experiments were used to examine the effects of TiO2 loading, ultraviolet–visible (UV) light, initial concentration, pH of aqueous solution on the hexavalent chromium (Cr(VI)) removal. The results show that TiO2 and UV irradiation could slow down the oxidation of nZVI during removing Cr(VI). The TiO2@nZVI with UV irradiation have dramatically higher Cr(VI) removal efficiencies than TiO2 and nZVI (increased by 78.5% and 39.9%, respectively). More Fe(II) instead of Fe(III) into the suspension and a slower oxidation rate of nZVI should be responsible for the enhanced Cr(VI) removal. Kinetic studies reveal that Cr(VI) adsorption process is accordant with the pseudo-second-order model, which suggests that chemisorption was the dominant adsorption mechanism. Langmuir isotherm adsorption model describes the Cr(VI) adsorption better and the maximum adsorption capacity of 62.80 mg·g−1. Finally, a possible removal and enhanced mechanism of Cr(VI) by TiO2@nZVI is proposed. Our study would provide ideas for the modification of nZVI and improve its removal efficiency for pollutants.

Photoadsorption of Cr(VI) on titanium dioxide modified by high-energy milling

Microcrystalline powders of rutile and anatase were milled in a high-energy planetary mill down to obtain nanosized TiO2 powders (the size of coherent scattering region (CSR) about 30 nm and 60 nm, respectively). The resulting powders were characterized by HRTEM, Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the ξ-potential of the aqueous suspensions was determined. High-energy milling made it possible to significantly increase the ability of TiO2 to remove chromium from aqueous solutions. The effectiveness of the powders for not only Cr(VI) removing but also total chromium adsorption under UV-irradiation and short wavelength visible light has been shown. This is important, since Cr(III) does not remain in the aqueous medium and cannot be oxidized back to Cr(VI) under the influence of some environmental factors. It is possible to remove more than 99.9% of total chromium and 100 % of chromium hexavalent from a 50 mg·L-1 solution of Cr(VI) using milled anatase. XPS showed that, upon the photoadsorption, Cr(VI) is reduced to Cr(III). The presence of an acetate buffer in the solution promotes the most efficient removal of chromium. This work shows a simple way to obtain a highly effective material with potential applications for the removal of high toxic hexavalent chromium from industrial wastewater. The milled anatase sample was successfully tested to remove Cr (VI) from a real wastewater sample.

Simultaneous Adsorptive/photocatalytic Removal of Organic Dyes and Hexavalent Chromium in Single and Binary Component Systems by Manganese Ferrite Nanoparticles

Background: As a major source of pollutant, the effluents of dye based industries are mostly associated with several toxic heavy metals. Limited efforts have been made on simultaneous removal of both dyes and heavy metals from these effluents through adsorption/photocatalysis processes. Spinel ferrites with narrow band gap and high stability are suitable for further exploitation in this regard. Objective: Synthesis and characterisation of manganese ferrite nanoparticle and to assess its efficiency towards removal of organic dyes and hexavalent chromium in single and binary component systems are the objectives of this study. Methods: Manganese ferrite nanoparticle (MF NPs), prepared by coprecipitation, was characterised systematically by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-Visible diffuse reflectance and magnetic measurement. Adsorptive and photocatalytic performances of the material under visible light were evaluated using aqueous solutions of different dyes and Cr(VI). Results: Characterisation by various techniques revealed the formation of cubic MF nanoparticles with narrow band gap (1.78 eV) and moderate saturation magnetization (38.5 emu/g). In comparison, the anionic dyes and Cr(VI) were better adsorbed on MF, while photoactivity was more pronounced in the case of cationic dye. Conclusion: MF NPs displayed potential for photo-degradation/reduction of different dyes and Cr(VI) individually or simultaneously under visible light. The catalyst can be recovered magnetically from the reaction mixture for recycling and further use.

Protonated-amino-functionalized bamboo hydrochar for efficient removal of hexavalent chromium and methyl orange

Hydrochar has great potential for wastewater treatment and the functional modification can significantly improve the ability of hydrochar to remove pollutants. Herein, a novel protonated amino-modified bamboo hydrochar (PAHC) was synthesized by the reaction of bamboo hydrochar first with acryloyl chloride, then with amine and finally with hydrochloric acid, and employed to adsorb methyl orange (MO) and Cr(VI). The PAHC was observed by BET, SEM-EDX, FTIR, elemental analysis, and zeta potential to monitor its textural properties before and after adsorption. The amino groups were effectively grafted onto the hydrochar by the Aza-Michael addition reaction through characterization. Adsorption results showed the PAHC possessed high MO/Cr(VI) adsorption amounts (515.35/523.57 ​mg ​g−1 ​at 298 ​K) because the introduction of protonated amine was pivotal in eliminating anionic pollutants by electrostatic interaction. The Langmuir/Freundlich model can well describe MO/Cr(VI) adsorption, which proves the removal process belongs to MO monolayer/Cr(VI) multilayer adsorption. The PAHC also exhibited a good regeneration performance. These results indicate the PAHC is a green and efficient adsorbent with potential application in wastewater treatment.

The study of removal chromium (VI) ions from aqueous solution by bimetallic ZnO/FeO nanocomposite with Siltstone: Isotherm, kinetics and reusability

In this study, nanocomposites of Baghanwala Siltstone (BSS) with ZnO (BSS/ZnO), FeO (BSS/FeO), and BSS/ZnO/FeO were successfully prepared for the removal of hexavalent chromium [(Cr (VI)] from aqueous solutions via a batch adsorption process. The characterization studies by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) found successful synthesis of the composites and demonstrated the occurrence of different active functional groups that played an active role in Cr ion adsorption. The effect of Cr initial concentrations (25–100 mg/L), adsorbent dose (0.5–2 g/L), pH (2–8), and contact time (0–160 min) on Cr remediation from contaminated water was examined. The order of Cr ion removal was BSS/ZnO/FeO (77-87%) > BSS/ZnO (74-83%) > BSS/FeO (71-77%) > BSS (68-74%). The as-synthesized BSS/ZnO/FeO led to successful Cr removal (87%) at a 25 mg/L Cr concentration at pH 4.0. The Cr ion adsorption by the BSS/ZnO/FeO nanocomposite was well explained by the Langmuir adsorption isotherm model (R2 > 0.99), while the kinetic experimental data was well fitted with the pseudo-second-order model (R2 > 0.99). Among the as-synthesized adsorbents, the BSS/ZnO/FeO nanocomposite showed excellent stability and reusability in seven sorption cycles. The results showed that the as-synthesized BSS/ZnO/FeO nanocomposite had the greatest adsorption potential for removing Cr ions from contaminated water.

Self-regulated S-scheme heterojunction for synergistic removal of tetracycline and hexavalent chromium: Synergistic mechanism of trivalent chromium

The limitation of conventional photocatalysts in simultaneously removing Tetracycline (TC), hexavalent chromium (Cr (VI)) and trivalent chromium (Cr (III)) were addressed in mixed pollution treatment. The S-scheme heterojunction of titanate nanotubes/Bi2WO6 (TNTs/BWO) was successfully constructed to achieve efficient removal of TC, Cr (VI), and Cr (III). The theoretical calculations (DFT) demonstrated that TNTs’ ion exchange properties led to the partial replacement of interlayer Na+ by Cr (III), optimizing the S-scheme heterojunction during the photocatalytic reaction. Experimental results revealed that the coexistence of TC, Cr (VI), and Cr (III) had a mutual promotion effect, as evidenced by the apparent rate constant of Cr (VI) reaching 0.7 min−1, which was 87.5 times higher than that of the single pollutant system, while maintaining a high apparent rate constant for TC. The likely intermediate products, degradation pathways, and photocatalytic mechanism were also elucidated using DFT molecular orbitals and Fukui index analysis. This work provides new insights and strategies for simultaneously removing pollutants and contributes to wastewater purification.

Comparative study for removal of toxic hexavalent chromium by zinc oxide nanoparticles, chitosan, chitin and zinc-chitosan nano-biocomposite

Hexavalent chromium is classified as a human carcinogen and its removal is crucial from wastewater. A comparative study was done to remove Cr (VI) from an aqueous solution by synthesized nanoparticles such as chitin, chitosan, zinc oxide (at various temperatures 500 °C, 600 °C and 700 °C), and ZnO-chitosan composite. Among all the synthesized materials the maximum uptake of chromium (VI) was observed in ZnO-chitosan nano-biocomposite (ZnO-CS NC). The adsorption variables like initial concentration, adsorbent dosage, adsorption time, and pH were examined. The batch adsorption studies revealed the best result in 20 ppm concentration dosage of 0.5 g/l, pH 3 at 60 min. The characterization of nanoparticles and nanocomposite was done by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared (FTIR) techniques Langmuir isotherm models were best fitted due to the highest R2 value. Among all adsorbent, ZnO-chitosan nano-biocomposite was best adsorbent for chromium (VI) removal. ZnO-chitosan adsorption capacity and adsorption efficiency were 69.5 mg/g and 96.5% respectively. ZnO nanoparticles showed the potential for antibacterial activity. Electrostatic attraction between chromium and ZnO-chitosan biocomposite was the main cause for the removal of chromium from aqueous solution and it could be a promising material for sustainable treatment of wastewater.

Accumulation mechanisms for contaminants on weak-base hybrid ion exchange resins

Mechanism of hexavalent chromium removal (Cr(VI) as CrO42-) by the weak-base ion exchange (IX) resin ResinTech® SIR-700-HP (SIR-700) from simulated groundwater is assessed in the presence of radioactive contaminants iodine-129 (as IO3-), uranium (U as uranyl UO22+), and technetium-99 (as TcO4-), and common environmental anions sulfate (SO42-) and chloride (Cl-). Batch tests using the acid sulfate form of SIR-700 demonstrated Cr(VI) and U(VI) removal exceeded 97%, except in the presence of high SO42- concentrations (536 mg/L) where Cr(VI) and U(VI) removal decreased to ≥ 80%. However, Cr(VI) removal notably improved with co-mingled U(VI) that complexes with SO42- at the protonated amine sites. These U–SO42- complexes are integral to U(VI) removal, as confirmed by the decrease in U(VI) removal (<40%) when the acid chloride form of SIR-700 was used instead. Solid phase characterization revealed that CrO42- is removed by IX with SO42- complexes and/or reduced to amorphous Cr(III)(OH)3 at secondary alcohol sites. Tc(VII)O4- and I(V)O3- also undergo chemical reduction, following a similar removal mechanism. Oxyanion removal preference is determined by the anion reduction potential (CrO42->TcO4->IO3-), geometry, and charge density. For these reasons, 39% and 69% of TcO4- and 17% and 39% of IO3- are removed in the presence and absence of Cr(VI), respectively.

Bacterial cellulose‐modified castor oil‐based polyurethane sponge for hexavalent chromium removal

AbstractDue to the multiple industrial applications of chromium compounds and their dangerous nature for the environment, the development of adsorbent materials has been investigated. In line with this reality, bacterial cellulose (BC) has become a potential filler in the polymeric matrix due to its ability to remove toxic metals; however, its performance is little explored. This research proposes a new approach for BC as a filler in castor oil‐based polyurethane, obtaining a sponge for Cr(VI) removal. The pure PU and PU + X%BC sponges (X stands for BC content between 5 and 20 wt%) were characterized by Fourier‐transform infrared spectroscopy, scanning electron microscopy, optical microscopy, density, contact angle (CA), and thermogravimetric analysis. Sorption capacity and efficiency were evaluated as a function of the fiber content, with tests performed in function of contact time (2.5 min to 3 h) at 50 mg L−1. The BC fillers of the sponges increased the density and influenced the morphological, chemical structural, thermal, and sorption properties. Thus, the sponge (PU + 20%BC) presented the highest CA (104.4°) and the best sorption capacity and efficiency (4.3 mg g−1 and 43.2%). The sorption mechanism was well‐defined by isotherm models, presenting a maximum adsorption capacity of 23.5 mg g−1 and best fit (R2 = 0.989) with the Freundlich isotherm. The sponge is an efficient material for Cr (VI) removal and provided a promising insight into an adsorption mechanism study.

Effects of zeta-potential on enhanced removal of hexavalent chromium by polypyrrole-graft-chitosan biodegradable copolymer

In the present research, chitosan grafted polypyrrole (PPy-g-CS) biodegradable copolymer particles were used as novel adsorbent to remove hexavalent chromium ions, Cr (VI), from water solutions and compared with the PPy. The effects of zeta (ζ)-potentials of these nanoparticles on the uptake properties of Cr(VI) ions were investigated as a function of pH. It was observed that the ζ-potential of PPy was shifted significantly from + 14 mV (pHinitial=4.8 for PPy) to + 47 mV (pHinitial=4.8 for PPy-g-CS) owing to the covalently grafting of polycationic CS chains with PPy chains. Thus, effective sites (−NH3+)for adsorption of Cr(VI) ions were created at the surfaces of the substrate. Adsorption efficiency of the PPy-g-CS copolymer observed to change by changing the pH of the medium which resulted in the variation of ζ-potential. The uptake capability of the PPy-g-CS copolymer increased compared to the pristine PPy. The maximum removal of Cr(VI) at the optimum pH of 4.8 and at 25 °C was 98 % and 73 % for PPy-g-CS and PPy, respectively. The adsorption kinetics was pseudo-second-order and inconsistent with the Freundlich isotherm. According to the thermodynamic parameters, the adsorption was endothermic (ΔH°PPy-g-CS = 7.12 kJ/mol), spontaneous (ΔG°PPy-g-CS = −546.43 kJ/mol) and driven by the increased entropy (ΔS°PPy-g-CS = 247.55 J/mol.K) of the system. In conclusion, the biodegradable PPy-g-CS graft copolymer particles with enhanced positive ζ-potential (+47 mV at pH=4.8) and adsorption capability (128 mg/g) would be a good candidate as an environmentally friendly adsorbent for the removal of negatively charged pollutants from water resources.

Structure and properties of nanoscale zero-valent iron supported on multimorphologies kaolinite and its enhanced removal of Cr(VI) from water

Kaolinite has various morphologies, stable chemical properties, and abundant reserves. To broaden its application in the environment, kaolinite-based nano zero-valent iron composite (nZVI/Kaol) was synthesized for the removal of hexavalent chromium (Cr(VI)) in water. The results showed that the removal rate of Cr(VI) by nZVI/Kaol (the Fe/Kaol mass ratio was 30%) reached 91.7% after 60 min reaction in Cr(VI) solution with an initial concentration of 20 mg/L (pH=7), while the removal efficiencies of Cr(VI) by nZVI and kaolinite were 34.5% and 5.6%. The characterization showed the different morphologies of kaolinite led to nZVI particles with uneven sizes loaded on the surface, that the size of nZVI loaded on rodlike kaolinite (50–100 nm) tended to be smaller than flaky kaolinite (150–200 nm), so the utilization of various sizes of nZVI enhanced Cr(VI) removal. The removal process matched the pseudo-second-order kinetic model and Langmuir isothermal adsorption model better. The results of thermodynamic calculation verified the removal of Cr(VI) by nZVI/Kaol to be endothermic. FTIR and XPS analysis showed that the removal mechanism of Cr(VI) by nZVI/Kaol included adsorption, redox and co-precipitation.

Preparation of waste face masks modified with MnO2/poly(m-phenylenediamine) as a novel adsorbent for hexavalent chromium removal: Comprehensive batch and column study

Single-use surgical face masks (SFM) have become one of the most used personal protective equipment (PPE) for preventing the transmission of diseases, especially COVID-19. However, the environment is being threatened by the huge amount of plastic waste generated by this material. In this study, a novel environmentally-friendly in-situ-surface polymerization method was employed to modify the surface of SFM with m-phenylenediamine (mPDA) for removing hexavalent chromium. The synthesized adsorbent was characterized by Field Emission-Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared Spectroscopy (FTIR). The investigations showed that the polymer and oxidant solution can be reused for several cycles, which was not possible in the conventional chemical polymerization method with ammonium persulfate (APS). The influence of various variables on the adsorption process was assessed and the optimum results was reported (adsorbent dosage: 3 g L−1, contact time: 60 min, pH: 2). The modeling investigations demonstrated that the process is followed by pseudo-second-order kinetic and University of Tehran (UT) isotherm model's assumptions, respectively. The obtained thermodynamic parameters at the investigated temperatures revealed the spontaneity and endothermic nature of Cr(VI) adsorption on the modified adsorbent. The column study was conducted and the impact of the flow rate and the feed concentration of Cr(VI) were evaluated. The experimental findings were analyzed using the Thomas model to discover how the concentration changes over time in the column operation. It was revealed that when the flow rate rose, the service volume declined.

Effect of modification with hydrobromic acid on the performance of activated carbon in the removal of hexavalent chromium from aqueous solution

AbstractThe ability of activated carbon from coconut shell to adsorb Cr(VI) from aqueous environment has been ameliorated by treating the carbon with hydrobromic acid. The best carbon is gained by soaking activated carbon in 0.3 mol L−1 HBr solution at 80°C for 13 h followed by being carbonized at 600°C in nitrogen for 1.5 h. The Cr(VI) adsorbed at equilibrium by the best as‐prepared carbon is 11.32 mg g−1 while that by the original one is 7.801 mg g−1. Characterization results manifest that the treatment with HBr solution leads to the increase of acidic groups and the decrease of basic groups on the carbon surface. The treatment with HBr solution produces many lactonic groups on the carbon. BET determination indicates that some micropores and mesopores are generated by the treatment with HBr solution. The increase of acidic groups and magnification of surface area is ascribed to the improvement of the ability to adsorb Cr(VI) ions. Lactonic groups and micropores play a key role in adsorbing Cr(VI) from water.

Removal of Hexavalent Chromium from Aqueous Solutions by Adsorption on Thermally Modified and Non-Modified Eggshells

Removal of heavy metals from waste water has received a great deal of attention. The compare Cr(VI) adsorption characteristics removing from wastewater by using thermally modified and non-modifiedeggshells were examined

Insights into the proton-enhanced mechanism of hexavalent chromium removal by amine polymers in strong acid wastewater: Reduction of hexavalent chromium and sequestration of trivalent chromium

Adsorption is a green technology of treating heavy metal-contaminated strong acid wastewaters for the recycling of heavy metal and reuse of strong acid. Herein, three amine polymers (APs) with different alkalinities and electron donating abilities were prepared to investigate the adsorption-reduction processes of Cr(VI). It was found that the removal of Cr(VI) was controlled by the concentration of –NRH+ on the surface of APs at pH > 2, which relies on the alkalinity of APs. However, the high concentration of NRH+ significantly facilitated the adsorption of Cr(VI) on the surface of APs and accelerated the mass transfer between Cr(VI) and APs at strong acid environment (pH ≤ 2). More importantly, the reduction of Cr(VI) was enhanced at pH ≤ 2, due to the high reduction potential of Cr(VI) (E ≥ 0.437). The ratio of reduction to adsorption (α) of Cr(VI) was above 0.70, and the proportion of Cr(III) bonding on Ph-AP excessed 67.6 %. Finally, a proton-enhanced mechanism of Cr(VI) removal was verified by analyzing FTIR and XPS spectra as well as constructing DFT model. This study provides a theoretical basis for the removal of Cr(VI) in the strong acid wastewater.

Comparative study of the effective removal of hexavalent chromium via calcium alginate and calcium alginate/Ulva fasciata composite

The present study revealed for the first time the removal of hexavalent chromium Cr(VI) with a high efficiency using an eco-friendly composite beads of alginate with the green alga Ulva fasciata compared to calcium alginate beads. This conclusion was reached in this study from the comparison of the removal efficiency of Cr(VI) by the well-known biosorbent material, calcium alginate (CA) with the studied calcium alginate/Ulva fasciata (CA/UF) biocomposite beads. The characterization of the prepared beads was achieved using several techniques such as Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray (EDAX). The Brunauer, Emmett, Teller (BET) and Barrett, Joyner, Halenda (BJH) analyses were also employed which indicated a three-fold increase in the surface area, a mean pore diameter of 2.3-fold and a total pore volume of 14-fold for calcium alginate/Ulva fasciata composite compared to calcium alginate beads. The results of batch experiments demonstrated the fast complete removal of Cr(VI) by the CA/UF composite compared to the maximum removal (75%) by CA. The Dubinin–Radushkevich isotherm model reflected the physical pore volume filling of Cr(VI) rather than adsorption on the pore walls, giving an adsorption mean free energy (2.24 kJ/mol) for CA/UF greater than that of CA (0.13 kJ/mol). Furthermore, Brunauer–Emmett–Teller isotherm reflected the multilayer adsorption for CA and CA/UF. Flory–Huggins isotherm model showed the more spontaneous adsorption for CA/UF than CA, with negative Gibbs free energy ΔG0 values of − 4.76 and − 6.91 kJ/mol, respectively. Whereas, Temkin isotherm model showed a higher adsorption binding energy of Cr(VI) on CA/UF than CA beads. In this study, the Langmuir model of Cr(VI) adsorption on CA/UF beads was the least applied among all studied adsorption isotherm models, which also revealed the multilayer adsorption mechanism of Cr(VI) ions. The Intra-particle diffusion model was applied for CA/UF composite beads, and this application suggested that the intra-particle diffusion is a part of the rate-limiting steps. The regeneration study showed a decrease in the adsorption efficiency of CA/UF composite from 97.4 to 82.3% for three consecutive cycles.

Removal of Cr(VI) from tanning wastewater using chitosan-SDS complexes in PEUF: Optimization and analysis via response surface methodology

In this study, we addressed the removal of hexavalent chromium (Cr(VI)), a highly toxic and soluble anionic heavy metal, using enhanced ultrafiltration (UF). The objective was to eliminate Cr(VI) species with molecular weights beyond the retention capability of standard UF membranes and achieve their retention through the incorporation of polymers and polymer-surfactant complexes within the UF membrane. Chitosan, a cationic polymer, and sodium lauryl sulfate (SDS), an anionic surfactant, were used in this context. The Cr(VI) solution was subjected to ultrafiltration in a laboratory-scale membrane cell, and its removal was assessed spectrophotometrically. Polymer and surfactant structures were characterized using turbidity, electrical conductivity, SEM-EDX, and FTIR analyses. Experimental studies were conducted using the face-centered central composite design (CCD) of the response surface methodology (RSM) to determine optimal removal and permeate flux values, as well as to unveil the relationships between the studied factors and the resulting responses.The results revealed that 100 % of the Cr(VI) species were removed from wastewater in the chitosan-based polymer-enhanced ultrafiltration (PEUF) study. With the chitosan-SDS complex, a removal efficiency of 98.33 % was achieved in synthetic wastewater. The PEUF study employing chitosan and the chitosan-SDS complex yielded permeate flux values of 30.73 L/h/m2 and 53.89 L/h/m2, respectively. The optimized conditions obtained from the models were then applied to real wastewater obtained from a leather industry tanning process. In the case of chitosan and the chitosan-SDS complex, the Cr(VI) removal efficiencies in the real wastewater were 4.40 % and 98.33 %, respectively.

Removal of hexavalent chromium from aqueous solution using low-cost magnetic microspheres derived from alkali-activated iron-rich copper slag

The utilization of iron-rich copper smelting waste residues is a promising method to treat chromium (Cr(VI)) contaminated wastewater. Improving its recoverability and adsorption efficiency in the adsorption process is the key to their effective utilization. Based on this, magnetic copper slag-based alkali-activated microspheres (CS-AAMs) with controllable particle size were prepared under the activation of sodium silicate by mechanical dispersion-suspension solidification method and used as an efficient low-cost magnetic adsorbent for Cr(VI) removal. The capability of CS-AAMs for Cr(VI) removal was investigated under different conditions. A maximum adsorption capacity of 32.5 mg/g was achieved at the pH of 1. The adsorption capacity can keep 89.25% after four cycles adsorption-desorption experiments. The adsorption process follows pseudo-first-order kinetics and occurs spontaneously with an endothermic nature. Both intraparticle diffusion and chemical complexation controlled the adsorption process. Notably, the electrostatic attraction between Cr(VI) and CS-AAMs played a key role in the adsorption of Cr(VI). The adsorbed Cr(VI) was complexed and partially reduced under the action of active Fe(II) species in CS-AAMs. The findings indicate that the CS-AAMs prepared in this study can efficiently adsorb Cr(VI) from industrial effluents.

Rose-inspired 3D 1T-MoS x /Ti3C2T x /TiO2 photocatalyst for water purification

The rose-inspired photocatalyst, 1T-MoS x /Ti3C2T x /TiO2, demonstrated exceptional activity in the simultaneous removal of hexavalent chromium (Cr(VI)) and methylene blue (MB), achieving high efficiencies of 97.7% and 97.2% respectively. Furthermore, it exhibited effective degradation of another dye, Rhodamine B (Rh.B). Scanning electron microscopy figures showed its unique nanoflower morphology. The introduction of titanium carbide nanosheets (Ti3C2T x ) and the formation of Schottky junctions can effectively prolong the carrier lifetime. The degradation path of MB was deduced by liquid chromatography–mass spectrometry, which confirmed the process of photocatalytic decomposition of organic pollutants. Compared to physical purification methods, it offers the advantage of not only removing pollutants but also degrading them. Furthermore, by utilizing MB as a sacrificial agent, the reduction can take place in a mild neutral environment, resulting in minimized secondary pollution. Through its distinctive three-dimensional structure and the Ti3C2T x cocatalyst, the 1T-MoS x /Ti3C2T x /TiO2 photocatalyst demonstrates remarkable catalytic activity, and effective purification of wastewater containing Cr(VI) and organic dyes.