Photocatalytic Reduction Of Hexavalent Chromium Research Articles

Nickel-decorated ZnO nanoparticles for effective solar reduction of hexavalent chromium and removal of selected pharmaceuticals

The efficient visible light driven photocatalytic reduction of hexavalent chromium, Cr(VI) was demonstrated using ZnO nanoparticles (NPs) decorated with oxo-clusters of transition metals. The ZnO NPs were synthesized by a facile one-pot solvothermal synthesis followed by a fast microwave-assisted (MW) grafting of transition metals on the surface of NPs. Nickel was found to be the most active transition metal for photocatalytic activity as demonstrated by reduction of Cr(VI) to Cr(III). The optimally grafted samples contained 0.5 wt% Ni and increased photocatalytic activity by almost one-fold. The oxo-clusters did not enter the lattice of ZnO but rather resided on the surface and their efficient bonding to the ZnO surface was proved by Raman, TEM and X-Ray absorption techniques. Influence of MW power was studied and shown that excessive power load leads to formation of elongated structures of ZnO which decreases the photocatalytic activity. It was demonstrated by measuring fluorescent radical products that electrons, efficiently transferred via oxygen, were the main active species in combination with the unchanged oxidation power of holes and •OH in the grafted samples. The applicability of the materials was tested in immobilized plug flow photoreactor system degrading five pharmaceuticals simultaneously where their long-term use was shown.

MoS2-CdS composite for photocatalytic reduction of hexavalent chromium and thin film optoelectronic device applications

We introduce an enhanced light-harvesting MoS2-based nanocomposite exhibiting improved solar light induced photocurrent generation, both in solution and solid phases. The MoS2-CdS composite was synthesized via easy to achieve, cost effective, two-step solution process for the photocatalytic potassium dichromate [Cr(VI)] reduction and photocurrent generation in thin-film optoelectronic devices. Incorporating 10 wt% MoS2 into the composite increased the degradation efficiency of CdS from 43.9 to 91.9%. Furthermore, the MoS2-CdS composite demonstrated a 2.88-fold increase in the degradation rate constant and a 2.15% enhancement in the apparent quantum yield compared to controlled CdS. Additionally, the electrical power consumption per order decrease in Cr(VI) reduced from 25.74 kWh m−3 for controlled CdS to 9 kWh m−3 aimed at 10 wt% MoS2-CdS composite, indicating optimal synergy between the counterparts of MoS2-CdS in its composite. The resulting thin-film device with 10 wt% MoS2-CdS exhibited robust photocurrent generation and nonlinear I–V characteristics under solar illumination, attributed to the unique electronic properties of the MoS2-CdS heterojunction, influencing carrier transport via band alignment and interface carrier trapping effects. Moreover, photocurrent generation increased linearly with illumination intensity, and dynamic photo response studies revealed rapid photocurrent generation under illumination. Furthermore, the optoelectronic key parameters of CdS, including photosensitivity, photoresponsivity, and detectivity, were enhanced by factors of 5.09, 3.33, and 12.3, respectively, upon composite formation with MoS2. This study offers novel insights into developing high-performance and cost-effective bimetallic sulfide photocatalysts for efficient solar light-induced photocurrent generation in both solution and solid phases.

Synergistic effects of sulfur vacancies and internal electric fields in FeS/MoS2 heterojunctions: A new approach to photocatalytic chromium removal

Molybdenum disulfide (MoS2) is heralded as an exemplary two-dimensional (2D) functional material, largely attributed to its distinctive layered structure. Upon forming heterojunctions with reducing species, MoS2 displays remarkable photocatalytic properties. In this research, we fabricated a novel heterojunction photocatalyst, FeS/MoS2-0.05, through the integration of FeS with hollow MoS2. This composite aims at the efficient photocatalytic reduction of hexavalent chromium (Cr(VI)). A comprehensive array of characterization techniques unveiled that MoS2 flakes, dispersed on FeS, provide numerous active sites for photocatalysis at the heterojunction interface. The inclusion of FeS seemingly promotes the formation of sulfur vacancies on MoS2. Consequently, this heterojunction catalyst exhibits photocatalytic activity surpassing pristine MoS2 by a factor of 3.77. The augmented activity of the FeS/MoS2-0.05 catalyst is attributed chiefly to an internal electric field at the interface. This field enhances the facilitation of charge transfer and separation significantly. Density functional theory (DFT) calculations, coupled with experimental analyses, corroborate this observation. Additionally, DFT calculations indicate that sulfur vacancies act as pivotal sites for Cr(VI) adsorption. Significantly, the adsorption energy of Cr(VI) species shows enhanced favorability under acidic conditions. Our results suggest that the FeS/MoS2-0.05 heterojunction photocatalyst presents substantial potential for the remediation of Cr(VI)-contaminated wastewater.

Development of Mn doped ZnAl2O4 via hydrothermal method as photocatalyst for Cr(VI) reduction under visible light

A hydrothermal method was employed to synthesise zinc aluminate oxides doped with manganese, with the aim of enhancing the photocatalytic reduction of hexavalent chromium to trivalent chromium. The optical, textural, microscopic, and structural features of the materials were assessed by a range of analytical techniques. These results revealed that incorporation of Mn dopant into the ZnAl2O4 (ZAO) reduced to band gap of ZAO and MD-ZAO are 3.56 and 2.79 eV, respectively. The best photoreduction efficiency was found with manganese-doped ZnAl2O4 (MD-ZAO) is 86.39 % than ZAO (69.38 %) after 120 min. The surface area study displays the 21.43 and 38.65 m2 g−1 for ZAO and MD-ZAO, respectively. When surface area of a nanomaterial is increased, a greater percentage of the material in contact with Cr ion, which increases the photocatalytic activity. A large interfacial area and pore volume aids in development of photoinduced electrons (e−) as well as hole pairs. The impedance study indicates the lower Rct value of ZAO and MD-ZAO are 0.45 Ω and 0.7 Ω, respectively. The finding indicates that Mn doped ZnAl2O4 work as excellent photocatalyst for photoreduction of hexavalent of Cr. The doped material can also act as potential catalyst in different future electrochemical and photocatalytic study.

LED-enhanced photocatalytic reduction of hexavalent chromium by Cu-doped ZnO nanorods: kinetic modeling, cost analysis, and toxicity assessment

ABSTRACT This study unveils the synthesis and application of Cu-doped ZnO nanorods (NRS) as an efficient catalyst for the photocatalytic reduction of hazardous hexavalent chromium (Cr6+) in water. Synthesized via a simplified co-precipitation method, the NRS demonstrated enhanced performance, achieving an 89.35% Cr6+ reduction efficiency under optimal conditions. The catalyst’s performance was significantly augmented in the presence of hydrogen peroxide (H2O2) and revealed a first-order kinetic model. Radical trapping experiments highlighted the pivotal role of hydroxyl radicals in the photocatalytic process. A comparative analysis of the NRS with LED/ZnO and undoped ZnO underscores the superior efficiency of the Cu-doped variant. Moreover, the applicability of this system was validated in real water and wastewater matrices containing Cr6+, indicating its promising potential for industrial and environmental applications. An in vivo bioassay using Daphnia magna further confirmed the reduced toxicity post-treatment, underscoring the environmental friendliness of this innovative approach. The findings present Cu-doped ZnO nanorods as a promising, effective, and eco-friendly catalyst for the remediation of Cr6+ contaminated water, marking a significant stride towards sustainable and efficient water treatment solutions.

Hydrothermal preparation of Nb5+-doped α-Fe2O3 nanorods for efficient visible light-driven photocatalytic reduction of hexavalent chromium

Nb5+ doped α-Fe2O3 (Nb-Fe2O3) nanorods with different Nb5+ contents were prepared using a low-temperature, short-time, one-pot hydrothermal method. All the prepared Nb-Fe2O3 products showed better photocatalytic activities than α-Fe2O3 nanorods in the reduction of aqueous Cr(VI) under visible light (wavelength > 420 nm). 4% Nb-Fe2O3 had the maximum photocatalytic activity, which was 2.24 times that of α-Fe2O3 nanorods and surpassed those of many newly reported visible light photocatalysts. Moreover, the photocatalytic efficiency of 4% Nb-Fe2O3 can be further improved by proper increasing its dosage, decreasing the initial pH and Cr(VI) concentration of K2Cr2O7 solution. Furthermore, 4% Nb-Fe2O3 showed rather good photocatalytic stability and reusability. Besides, 4% Nb-Fe2O3 was efficient in visible light-driven photocatalytic reduction of Cr(VI) in diluted black chrome plating solution. Nb5+-doping can efficaciously enhance the abilities of α-Fe2O3 in absorbing visible light and transferring and separating photogenerated carriers, thereby contributing to the elevated photocatalytic activity of Nb-Fe2O3.

Photocatalytic reduction of hexavalent chromium using Zn2SnO4–ZnO modified g-C3N4 composite

In this study, a novel hierarchical g-C3N4/Zn2SnO4–ZnO heterojunction system was reported as an efficient photocatalyst for the reduction of Cr(VI). The fabrication of the composite involved the synthesis of the complex metal oxide (Zn2SnO4–ZnO), followed by the in-situ integration into graphitic carbon nitride. The structure, morphology, and optical properties of the as-prepared tertiary composite were determined using various analytical techniques. The results indicated the improvement in surface area and the electronic structure of the semiconductor heterostructures. Photocatalytic measurement showed the efficiency of the ternary composite to cause a reduction of the band gap energy, delayed charge recombination process and enhancement of the visible light absorption. Reaction parameters including the solution pH, photocatalyst (g-C3N4/ZTO-ZnO) dosage, and the initial concentration of Cr(VI) on the degradation efficiency of the photocatalyst were evaluated. The solution pH was varied from 2 to 8, and pH 2 displayed the highest removal of Cr(VI) with 99.2 % removal efficiency for the g-C3N4/ZTO-ZnO, while the ZTO-ZnO exhibited 72 % efficiency. Finally, the kinetic study of the photocatalytic reaction showed an increase in the overall rate constant k with the increase in initial concentration of Cr(VI). The outstanding performance of the ternary composite compared to the bare complex metal oxide makes the innovative g-C3N4/Zn2SnO4–ZnO composite a promising material for the removal of Cr(VI) from aquatic environment.

Efficient Photocatalytic Reduction of Hexavalent Chromium by BiVO4-Decorated MXene Photocatalysts and Their Charge Carrier Dynamics.

The synergistically MXene (Ti3C2Tx) co-catalyst-decorated BiVO4-based heterostructured photocatalysts have been synthesized by a hydrothermal approach with varied loading concentrations of MXene (Ti3C2Tx) to drive the hexavalent chromium reduction efficiently. The formation of the heterostructured photocatalyst was confirmed by the appearance of X-ray diffraction (XRD) peaks corresponding to the monoclinic BiVO4 phase and MXene (Ti3C2Tx) and also the antisymmetric (834 cm-1) and symmetric stretching (715 cm-1) of tetrahedral VO4 and D (1330 cm-1) and G (1570 cm-1) bands corresponding to MXene (Ti3C2Tx) in the Raman spectrum. The worm-like structures of BiVO4 nanocrystals grew onto the lamellar sheets of MXene (Ti3C2Tx), as shown by field emission scanning electron microscopy (FESEM), and has an increased surface area of 15.62 m2g-1 in the case of BVO-20-TC. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of V5+ and Ti3+states, and the uniform distribution of BiVO4 nanocrystals over lamellar sheets of MXene (Ti3C2Tx) is evident from energy-dispersive X-ray (EDX) analysis. The ultraviolet-diffuse reflectance spectroscopy (UV-DRS) spectra suggest a decrease in the band gap energy of BVO-20-TC to 2.335 eV, promoting a higher degree of visible light harvesting. Upon optimization, by varying the pH, the amount of the photocatalyst, and the concentration of Cr(IV), BVO-20-TC exhibits the highest photocatalytic efficiency (96.39%) while using a Cr(VI) concentration of 10 ppm at pH 2 and 15 mg of the photocatalyst, and the photoreduction of Cr(VI) to Cr(III) follows the pseudo-first-order reaction. The decrease in the PL intensity in BVO-20-TC reveals a faster transfer of electrons from MXene (Ti3C2Tx) to BiVO4. Further, the higher degree of band bending at the BiVO4/MXene (Ti3C2Tx) heterojunction, revealed from the Mott-Schottky analysis, facilitates efficient charge transfer and eventually faster and efficient photoreduction of Cr(VI) to Cr(III). The reusability and stability test undertaken for BVO-20-TC reveals that even after five cycles, the Cr (VI) photoreduction efficacy is retained. This work provides insights into photoreduction of Cr (VI) by using such heterostructures.

Synergistic Photocatalytic Reduction of Hexavalent Chromium Using Graphene Quantum Dots and Formic Acid Optimization and Kinetics

Synergistic Photocatalytic Reduction of Hexavalent Chromium Using Graphene Quantum Dots and Formic Acid Optimization and Kinetics

Rapid photocatalytic reduction of hexavalent chromium over Z-scheme MgIn2S4/BiPO4 heterojunction: Performance, DFT calculation and mechanism insight

The accumulation of highly fluid and biotoxic hexavalent chromium (Cr(VI)) impairs water ecosystems. It is urgent to quickly reduce Cr (VI) to trivalent chromium (Cr (III)) in wastewater. Hereby, Z-scheme MgIn2S4/BiPO4 heterojunction was prepared, and MB-30 (mass ratio of BiPO4 to composite) presented a rapid Cr(VI) (10 mg L−1) removal efficiency of 100% within 10 min, its kinetic rate constant was 9.0 and 30.1 folds that of MgIn2S4 and BiPO4, respectively. After four rounds, MB-30 maintained a high removal rate of 93.18% and stabilized crystal texture. First-principles calculations revealed that the formation of Z-scheme heterojunction could ameliorate charge generation, detachment, migration capability, and light utilization. Meanwhile, the coupling of S and O in the two components produced a tight S–O bond, which acted as an atomic-level access to promote carrier migration. The findings were consistent with the structure superiority and optical and electronic properties of MB-30. The Z-scheme pattern was substantiated based on multifarious experiments, which exhibited an elevated reduction potential while emphasizing the significance of interfacial chemical bond and the internal electric field (IEF) on carrier detachment and migration.

Bi-functional photocatalytic heterostructures combining titania thin films with carbon quantum dots (C-QDs/TiO2) for effective elimination of water pollutants

In this study, carbon quantum dots (C-QDs), prepared via hydrothermal-microwave procedures, were successfully combined with nanostructured titania (TiO2). The photocatalytic oxidation/reduction activity of the C-QDs/TiO2 composite films was evaluated in the decomposition of organic-inorganic contaminants from aqueous solutions under UV illumination. Physicochemical characterizations were applied to investigate the crystal structure of the carbon quantum dots and the composites. It was found that the prepared C-QDs/TiO2 composites had great contribution to the photocatalytic reduction of hexavalent chromium (Cr+6) species and 4-Nitrophenol (PNP) as well as to the photocatalytic oxidation of methylene blue (MB) and Rhodamine B (RhB) dyes. The mechanism of the photocatalytic reaction was studied with trapping experiments, revealing that the electron (e−) radical species were powerfully supported for the photocatalytic reduction of Cr+6 and PNP and the holes (h+) are the main active species for the photocatalytic oxidation reactions.

Bio-reduced Ag nanoparticle decorated on ZnO for enhancement of photocatalytic reduction of hexavalent chromium and photocatalytic degradation of rhodamine B

Ag nanoparticles reduced by organic components extracted from Jasmine tea leaves were decorated by a hydrothermal reaction on ZnO to fabricate AgNPs@ZnO composite, and then the composite was applied for photocatalytic reactions to degrade rhodamine B (RhB) and reduce hexavalent chromium (Cr(VI)). The produced composite (AgNPs@ZnO) was optically and physicochemically characterized to better understand the impact of the development of the AgNPs-ZnO heterojunction when compared to that of pure ZnO. The optimized AgNPs@ZnO reduced more than 95% of 10 mg/L Cr(VI) in 60 min and degraded more than 95% of 10 mg/L RhB in 180 min, with a rate constant around five times for Cr reduction and three times for RhB degradation faster than that of pure ZnO, due to its superior capacity to separate and transport photogenerated electron-hole pairs, as evidenced by a drop in photoluminescence intensity. Furthermore, when AgNPs were placed on the surface of ZnO in the composites, surface defects were generated on ZnO, as confirmed by the energy-resolved distribution of electron trap (ERDT) pattern for AgNPs@ZnO, indicating the formation of new electron trapping levels. This might cause a reduction of the energy band gap, resulting in the enhancement of light adsorption and reduction of charge recombination. Therefore, the present bio-induced composite of AgNPs@ZnO opens up new possibilities for photochemical purification technology in aquatic environments.

Insight into the photocatalytic reduction of hexavalent chromium using photodeposited metal nanoparticle-TiO2 photocatalysis.

Hexavalent chromium (Cr(VI)) is carcinogenic to organisms. It is widely used in several industries. In this work, we investigated the Cr(VI) photocatalytic reaction with a scavenger on Pt and Cu-TiO2 photocatalysts. Metal-deposited TiO2 was successfully synthesized by a photodeposition method. TEM-EDX, XRD, and UV-DR were analyzed to study the changes in morphology, crystallinity, and the electronic properties of photocatalysts. The rate of charge recombination during reduction and photoluminescence (PL) spectroscopy was used to examine the catalysts in depth. Cu-TiO2 demonstrates the highest photocatalytic activity for 63.74% of Cr(VI) removal. To understand the photoreduction of Cr(VI), the fate transformation of Cr species during the adsorption and reaction was investigated using in situ XANES. The results demonstrated that the Cr(III) was noticeably main component adsorbed over the catalyst, particularly in Cu-TiO2. The presence of humic acid can boost the Cr(VI) removal efficiency and enhanced the Cr(VI) reduction to Cr(III). We believe that the extensive research on Cr(VI) photoreduction on metal-TiO2 heterojunction will provide a comprehensive understanding of catalytic behaviors, paving the way for rationally designed novel Cr reduction catalysts.

A facile synthesis of ternary hybrid nanocomposite of WS2/ZnO/PPy: An efficient photocatalyst for the degradation of chromium hexavalent

In this study novel and promising ternary hybrid nanocomposite of tungsten disulphide (WS2), zinc oxide (ZnO) and polypyrrole (PPy) has been synthesized for the efficacious photocatalytic reduction of hexavalent chromium (Cr(VI)). This ternary hybrid nanocomposite was prepared using the hydrothermal and in situ oxidative polymerization method. The crystal structures, physicochemical and optical features of the prepared nanocomposite were examined using various characterization techniques such as XRD, FTIR, and UV–Vis spectroscopy. The synthesized nanocomposite contains the morphologies of pristine samples such as nanosheets, nanorods and nanoparticles of WS2, ZnO and PPy, respectively as demonstrated from FESEM images. The adsorption and photocatalytic degradation studies were performed as a function of concentrations of Cr (VI). The synthesized nanocomposite shows enhanced degradation efficiency (81.82%–94.66%) from pristine samples (1.81–4.85% for WS2, 29.09–36.36% for ZnO and 45.55–48.94% for PPy) towards 10 mg/L concentration of Cr(VI) under dark and light conditions, respectively. This enhanced degradation efficiency was attributed to the large surface area, lower recombination rate for photogenerated species, superior absorption for light and generation of free radicals under dark and light conditions as explained by TCSPC decay, tauc's plot (2.28 eV) and EPR measurements, respectively. EPR and scavenger study both supports for the formation of free radicals (•O2−) and (.OH) in light and dark both conditions. The value of g-factor comes out to be 2.01 from EPR study. The kinetic study illustrates that the photocatalytic degradation of Cr(VI) by the prepared ternary nanocomposite followed pseudo-second-order rate kinetics model and Langmuir adsorption isotherm. These models proposed that the removal of Cr(VI) was take place through both physisorption and chemisorption processes. The degradation mechanism was analyzed with the help of Mott-Schottky/scavenger studies, and revealed that the superoxide radicals (•O2−) were the primary active species. The reusability experiment demonstrates that the prepared nanocomposite can be reused up to 5 times with almost the same efficiency in all cycles and hence, can be considered as a promising candidate for wastewater treatment.

A novel TiO2-x/TiN@ACB composite for synchronous photocatalytic Cr(VI) reduction and water photothermal evaporation under visible/infrared light illumination

Relatively large band-gap, fast charge carriers recombination, and mono-functionality of photocatalytic materials are still representing stumbling hurdles against their optimal usage for water cleaning. Herein, a novel black titanium oxide/plasmonic titanium nitride@activated coconut biochar (TiO2-x/TiN@ACB) composite was designed to have both photocatalytic and photothermal functions. Intermediate states of black TiO2-x, plasmonic effect of TiN, and high electrons (e−) capacity of biochar enhanced band-gap narrowing, light absorbance extension, and charge carriers separation respectively. Black TiO2-x and plasmonic TiN sensitization via visible/infrared (Vis/IR) portion of photonic spectrum in addition to the confirmed close contact of composite constituents explained the demonstrated major role of e− in photocatalytic mechanism through efficient excitation and facile transfer. Thanks to black photocatalytic semiconductor and carbonic materials for their ultimate photons harnessing and efficient photothermal conversion where the composite exhibited a remarkable photothermal water evaporation upon Vis/IR illumination as well. TiO2-x/TiN@ACB composite revealed 92.8 and 89.7% photocatalytic reduction of hexavalent chromium (Cr(VI)) and water evaporation efficiencies up to 92.9 and 51.1% upon IR and Vis light illumination respectively. This study proposes a new approach for efficient water cleaning by coupling of oxygen deficient and plasmonic semiconductors supported on naturally derived carbonic material as a broad spectrum harvester and bi-functional photocatalytic and photothermal material.

Constructing an acidic microenvironment by sulfonated polymers for photocatalytic reduction of hexavalent chromium under neutral conditions

Hexavalent chromium (VI) heavy metal contamination is considered a serious threat to human health and the environment. The photocatalytic reduction of Cr(VI) basically occurs in the acidic environment, severely limiting the application of photocatalysts for the reduction of Cr(VI). Therefore, we designed a microenvironment strategy to achieve efficient reduction of Cr (VI) under neutral conditions by introducing sulfonic acid onto the aromatic conjugated skeleton. A series of characterizations and experiments have shown that the sulfonated aromatic ring conjugated polymer (Arcp-SO3H) can efficiently remove Cr(VI) under neutral or even alkaline conditions. In neutral solutions, Arcp-SO3H has a rate constant of 0.054 min−1 within 90 min and has an efficiency of nearly 100 %, which is 16 times faster than before sulfonation (k = 0.0316 min−1). the Arcp-SO3H surpasses all organic polymers and most metal-based photocatalysts in the related field. The capture experiments have proved that •O2– is the main role of reducing Cr(VI), and e- is secondary, which is quite different from the mechanism reported in the previous literature. The efficiency of reducing Cr (VI) in the four-cycle experiment is still 96 %, which also proves that Arcp-SO3H has strong stability and reproducibility. Thus, Arcp-SO3H has great practical application potential in the treatment of wastewater, and microenvironmental strategies also offer new possibilities in the field of environmental remediation.

BiOBr microspheres anchored with Cu2O nanoparticles and rGO: A Z-scheme heterojunction photocatalyst for efficient reduction of Cr(VI) under visible light irradiation

Photocatalytic reduction of hexavalent chromium (Cr(VI)) is an effective way to reduce its environmental risk. However, it remains a challenge to achieve a high removal rate in mild conditions. In order to efficiently remove Cr(VI) from water, a novel Z-scheme heterojunction composite photocatalyst rCB-20 (Cu2O/rGO/BiOBr, 20% Cu2O) was successfully prepared using a simple two-step strategy in this work. The characterizations of the catalyst show that the Z-scheme heterojunction formed between Cu2O and BiOBr is favorable for facilitating the separation of photogenerated carriers. The existence of rGO can reduce the resistance of electron transport. Therefore, the composite photocatalyst exhibits a very high photocatalytic activity in the photoreduction of Cr(VI). For example, using it to completely remove Cr(VI) with a concentration of 20 mg•L−1 in the pH = 4 solution only requires 40 min. Even the complete removal of the same concentration of Cr(VI) in neutral water at pH 7 does not take more than 90 min. Meanwhile, it possesses a high stability in catalytic activity and structure.

Photocatalytic Reduction of Hexavalent Chromium Using Cu3.21Bi4.79S9/g-C3N4 Nanocomposite

The photocatalytic reduction of hexavalent chromium, Cr(VI), to the trivalent species, Cr(III), has continued to inspire the synthesis of novel photocatalysts that are capable of achieving the task of converting Cr(VI) to the less toxic and more useful species. In this study, a novel functionalized graphitic carbon nitride (Cu3.21Bi4.79S9/gC3N4) was synthesized and characterized by using X-ray diffraction (XRD), thermogravimetry analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). The composite was used for the photocatalytic reduction of hexavalent chromium, Cr(VI), under visible light irradiation. A 92.77% efficiency of the reduction was achieved at pH 2, using about 10 mg of the photocatalyst and 10 mg/L of the Cr(VI) solution. A pseudo-first-order kinetic study indicated 0.0076 min−1, 0.0286 min−1, and 0.0393 min−1 rate constants for the nanoparticles, pristine gC3N4, and the nanocomposite, respectively. This indicated an enhancement in the rate of reduction by the functionalized gC3N4 by 1.37- and 5.17-fold compared to the pristine gC3N4 and Cu3.21Bi4.79S9, respectively. A study of how the presence of other contaminants including dye (bisphenol A) and heavy-metal ions (Ag(I) and Pb(II)) in the system affects the photocatalytic process showed a reduction in the rate from 0.0393 min−1 to 0.0019 min−1 and 0.0039 min−1, respectively. Finally, the radical scavenging experiments showed that the main active species for the photocatalytic reduction of Cr(VI) are electrons (e−), hydroxyl radicals (·OH−), and superoxide (·O2−). This study shows the potential of functionalized gC3N4 as sustainable materials in the removal of hexavalent Cr from an aqueous solution.

Synthesis of ZnO/Ag/phosphorene for photocatalytic reduction of hexavalent chromium (Cr-VI)

Synthesis of ZnO/Ag/phosphorene for photocatalytic reduction of hexavalent chromium (Cr-VI)

Ag-modified g-C3N4 with enhanced activity for the photocatalytic reduction of hexavalent chromium in the presence of EDTA under ultraviolet irradiation

ABSTRACT The photocatalytic reduction of Cr6+ to Cr3+ in an aqueous solution, using 3 wt% Ag/g-C3N4 in the presence of ethylenediaminetetraacetic acid (EDTA), has been investigated here. The photocatalytic reduction of Cr6+ with pure g-C3N4 was very low. The addition of Ag and EDTA can significantly improve the photocatalytic reduction of Cr6+ using g-C3N4. In the presence of EDTA, the efficiency with Ag/g-C3N4 was better than those with Au/g-C3N4 and Cu/g-C3N4. With EDTA, the reduction rate constant increased from 0.0005 for pure g-C3N4 to 0.12 min−1 for 3 wt% Ag/g-C3N4. By increasing the concentration of EDTA from 0 to 500 mg L−1, the reduction efficiency of Cr6+ increased extremely, and the rate constant raised from 0.008 to 0.12 min−1. The optimal EDTA concentration was 500 mg L−1 for the photocatalyst Ag/g-C3N4. The Ag-EDTA complex may be reduced to metallic silver by the conduction band electrons of g-C3N4. The electron–hole recombination was significantly suppressed by the electron trapping of Ag. EDTA may act in by the formation of Cr3+-complex and the separation of Cr3+ from the g-C3N4 surface and by the valence band hole scavenger of g-C3N4. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL) were used to characterize g-C3N4 and Ag/g-C3N4 nanoparticles. A possible mechanism for photocatalytic Cr6+ reduction has also been demonstrated.