Performance For Reduction Of Cr Research Articles

Treated activated carbon as a metal-free catalyst for effectively catalytic reduction of toxic hexavalent chromium

In this work, activated carbon treated in N2 atmosphere, as a non-metallic catalyst, exhibits excellent catalytic performance in reduction of Cr (VI) to Cr (III) using HCOOH as the reducing agent at room temperature. A series of characterizations and control experiments were carried out to deduce the possible reaction mechanism. The results showed that the improved catalytic performance can be attributed to the enhanced graphitization degree and basic sites such as pyrone-like, which favor electron transferring and activation of reactant. The reaction rate constant observed herein for the C-800 was 22 and 6 times more than that for C-0 and Pd/C catalyst, respectively. In addition, C-800 showed good recycle performance, and no loss of activity was observed after 5 cycles. This study broadens the application of nonmetallic catalyst and provides an easy-available and cost-effective catalytic material for removing toxic Cr (VI).

Evaluation of a visible light-responsive polyaniline nanofiber˗cadmium sulfide quantum dots photocathode for simultaneous hexavalent chromium reduction and electricity generation in photo-microbial fuel cell

Photo˗microbial fuel cells (Photo˗MFCs) technology have been utilized for cathodic reduction of hexavalent chromium (Cr(VI)) in wastewater and simultaneously electricity generation by using a photocathode. In the present manuscript, polyaniline nanofiber (PANI)˗CdS Quantum Dots (QDs) photocathode is prepared via an in˗situ method to investigate its performance for reduction of Cr(VI) from wastewaters in Photo˗MFC. The structural and optical analyses confirm the enhanced construction and photocatalytic properties of the nanocomposite with high absorption in the visible range. The selected photocathode is also characterized by photo˗electrochemical techniques to determine its sensitivity to visible light. In the photoreduction process, the Photo˗MFC system equipped with the PANI˗CdS QDs photocathode has acquired an outstanding reduction ratio up to 97.4% at a pH value of 2, an initial concentration of 10 mg/L, within illumination time of 8 h and these results follow a pseudo-second˗order kinetics with a constant of 0.081 mgL ˗1 h ˗1 , as well. Meanwhile, the Photo˗MFC achieves the highest maximum power density of 166.93 mW.m −2 in the presence of visible light. The present study has successfully confirmed that, Photo˗MFC equipped with a PANI˗CdS QDs photocathode, can be a promising technology for the reduction of Cr(VI) with an enhanced output power generation simultaneously. • Polyaniline-CdS Quantum Dots photocathode is prepared via an in-situ method. • Photocathode is utilized for the reduction of Cr(VI) in a Photo-MFC. • Simultaneous electricity generation is evaluated in the Photo-MFC. • Photo-MFC equipped with PANI-CdS QDs achieves the reduction efficiency up 97.4%. • Photo-MFC achieves the highest power density with the visible light illumination.

Palladium nanoparticles uniformly and firmly supported on hierarchical flower-like TiO2 nanospheres as a highly active and reusable catalyst for detoxification of Cr(VI)-contaminated water

The rational design of highly active and stable nanocatalysts towards the detoxification of Cr(VI)-contaminated water is of great importance for environmental remediation. In the present work, a novel Pd-based hybrid nanomaterial, composed of Pd nanoparticles (Pd NPs) supported on three-dimensional hierarchical titania nanoflowers (fTiO2), was fabricated and systematically investigated as the catalyst of chromium detoxification. Pd NPs with diameter of ~ 2.8 nm were found to be uniformly and firmly supported onto the crystalline nanosheets of fTiO2. More importantly, the highly open porous flower-like architecture of Pd NPs/fTiO2 could not only endow the catalyst with high surface area (237.5 m2 g−1) and large pore volume (0.86 cm3 g−1), but also facilitate reactant diffusion and exposure of active sites. Benefitting from these remarkable features, the Pd NPs/fTiO2 exhibited superior catalytic performance for reduction of Cr(VI) in the presence of formic acid. The TOF reached up to 633.0 h−1, which was several and even more than one hundred times as high as those obtained by previously reported supported Pd-based catalysts. Moreover, the catalytic activity of Pd NPs/fTiO2 could remain almost unchanged after being recycled several times, demonstrating its long-term stability. Therefore, the Pd NPs/fTiO2 would be promising for practical wastewater treatment.

Design and synthesis of Mo2C/MoO3 with enhanced visible-light photocatalytic performance for reduction of Cr (VI) and degradation of organic pollutants

In this study, a facile impregnation-calcination strategy was applied in order to synthesize Mo2C modified MoO3 (Mo2C/MoO3), which was then employed as catalyst for the photoreduction of Cr (VI) and photodegradation of methyl orange (MO) upon irradiation by visible light (λ > 400 nm). The apparent rate constant (k) of Mo2C/MoO3 for the MO photocatalyzed degradation reaction under visible-light irradiation was found to be 0.0171 min-1, which was 4.59 and 67.38 times higher than that of Pt/MoO3 and pristine MoO3, respectively. Study of the photocatalytic mechanism revealed that the •O2- species played a major role in MO degradation. Moreover, the addition of Mo2C enhanced the light response region of MoO3, and also promoted the photocatalytic activity of MoO3. This was due to the enhanced separation efficiency of photogenerated electron-hole pairs and broader photoresponse region. This work suggests a new use for the easily accessible Mo2C/MoO3 heterostructure and could facilitate the application of photocatalysts for wastewater treatment．

High carbon iron filings (HCIF) and metal reducing bacteria (Serratia sp.) co-assisted Cr (VI) reduction: Kinetics, mechanism and longevity

Permeable reactive barriers (PRBs) have been an area of interest for in-situ remediation of groundwater. However, the corrosion of iron used in PRBs has been an area of concern. This study was aimed to enhance the long term performance for reduction of Cr (VI) by high carbon iron filings (HCIF) co-assisted with Serratia sp. Cr (VI) reduction by HCIF alone followed pseudo-first order kinetics and the reaction rate was 0.382 h−1 for 50 mg/L of Cr (VI) which declined to 0.0017 mg−1 L h−1 in combined system. But in cyclic studies, the reduction of Cr (VI) with HCIF alone system declined to 70% after 2 cycles whereas more than 90% reduction was observed in combined system up to four cycles. The corrosion potential and XRD data supported that Serratia sp. have positive effect on longevity of HCIF for Cr (VI) reduction.

Mesoporous carbon black as a metal-free electrocatalyst for highly effective determination of chromium(VI)

Hexavalent chromium is one of most toxic heavy metal contaminants in biological and environmental systems, thus the electrochemical method with high-sensitivity, excellent-accuracy, low-cost and easy-operation is desired to be developed for detecting Cr(VI). In this work, carbon black (CB) modified glassy carbon electrode (GCE), was proposed as a sensor for monitoring Cr(VI) concentrations. CB is cheap, green, environmentally friendly, and incapable to secondary pollution. Moreover, the sp2-bonded CB possesses a great plenty of mesopores as the charge transport channels in interior surface to enhance the sensing efficiency. Thus CB modified GCE demonstrated an outstanding electrocatalytic performance for reduction of Cr(VI), with a wide linear concentration range from 0.025 to 483.225μM and a low detection limit (LOD) of 10nM. The modified electrode also showed fast response, high stability, as well as good selectivity against interferences from other metal ions. These attributes suggest that CB as a metal-free electrocatalyst has an exciting prospects of sensing applications for determination of Cr(VI).

Investigation of photocatalytic activities over ZnO–TiO2–reduced graphene oxide composites synthesized via microwave-assisted reaction

ZnO–TiO2–reduced graphene oxide (RGO) composites were successfully synthesized by microwave-assisted reduction of graphite oxide in ZnO precursor solution with TiO2 suspension using a microwave synthesis system. Their morphology, structure, and photocatalytic performance in the reduction of Cr(VI) were characterized by scanning electron microscopy, X-ray diffraction spectroscopy, and UV–vis absorption spectrophotometer. The results show that ZnO–TiO2–RGO composites exhibit an enhanced photocatalytic performance in reduction of Cr(VI) with a maximum removal rate of 99.4% under UV light irradiation as compared with pure ZnO (58%) and ZnO–RGO (98%) composites due to the increased light absorption intensity and the reduction of electron–hole pair recombination in ZnO with the introduction of TiO2.

Sol–gel synthesis of Au/N–TiO2 composite for photocatalytic reduction of Cr(vi)

Au/N–TiO2 composites are successfully synthesized via a modified sol–gel method and their photocatalytic performance in reduction of Cr(VI) is investigated. Au/N–TiO2 composites exhibit an enhanced photocatalytic performance in the reduction of Cr(VI) with a maximum reduction rate of 90% under visible light irradiation as compared with pure TiO2 (34%) and N–TiO2 (80%) due to the increase of light absorption intensity and range as well as the reduction of electron–hole pair recombination in TiO2 with the incorporation of N and Au.

UV-assisted photocatalytic synthesis of ZnO–reduced graphene oxide composites with enhanced photocatalytic activity in reduction of Cr(VI)

ZnO–reduced graphene oxide (RGO) composites are successfully synthesized via UV-assisted photocatalytic reduction of graphite oxide by ZnO nanoparticles in ethanol. Their morphology, structure and photocatalytic performance in reduction of Cr(VI) are characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction spectroscopy, UV–vis absorption spectrophotometer, respectively. The results show that in the composites the RGO nanosheets are decorated densely by ZnO nanoparticles, which displays a good combination between RGO and ZnO. ZnO–RGO composites exhibit an enhanced photocatalytic performance in reduction of Cr(VI) with a maximum removal rate of 96% under UV light irradiation as compared with pure ZnO (67%) due to the increased light absorption intensity and range as well as the reduction of electron–hole pair recombination in ZnO with the introduction of RGO.

Microwave-assisted synthesis of ZnO–graphene composite for photocatalytic reduction of Cr(vi)

ZnO–graphene composites are successfully synthesized via microwave-assisted reaction of zinc sulfate in aqueous solution with a graphite oxide dispersion using a microwave synthesis system. Their morphology, structure and photocatalytic performance in reduction of Cr(VI) are characterized by scanning electron microscopy, X-ray diffraction spectroscopy and UV-vis absorption spectrophotometer, respectively. The results show that in the composite the graphene nanosheets are decorated densely by ZnO nanosheets, which display a good combination between graphene and ZnO nanosheets. The ZnO–graphene composite exhibits an enhanced photocatalytic performance in the reduction of Cr(VI) with a removal rate of 98% under UV light irradiation as compared with pure ZnO (58%) due to the increased light absorption intensity and range, as well as the reduction of electron–hole pair recombination with the introduction of graphene.