Photocatalyst For Reduction Of Cr Research Articles

Synthesis of Zn0.1Sn0.1Cd0.8Sx Solid Solutions for Photocatalytic Reduction of Cr(VI): Bandgap Structure and Sulfur Vacancy Regulation.

Ternary metal sulfides (TMSs) solid solutions have been regarded as ideal semiconductors in various photocatalytic reactions due to theiroutstanding redox reversibility, high electron conductivity, and great stability. In this work, a series of Zn0.1Sn0.1Cd0.8S x (ZSCS) solid solutions were synthesized by a simple hydrothermal methodand applied in the photocatalytic reduction of Cr(VI). The Cr(VI) reduction efficiency of ZSCS-5 quickly reached nearly 100% within 3 min under visible light irradiation. The controlling of sulfur content in ZSCS induced the transformation of cubic to hexagonal CdS, regulating the energy band structure and sulfur vacancy (SV) content, both of which further influenced the redox properties of ZSCS samples. The morenegativeconduction band position and more sulfur vacancies contributed to the enhanced photocatalytic reduction performance of ZSCS-5 toward Cr(VI). The active species 1O2, O2•－,and e－were all involved and 1O2played a pivotal rolein the photocatalytic reaction. This work provided an excellent photocatalyst for reduction of Cr(VI) and strongly confirmed the regulation of energy band structure and sulfur vacancies in photocatalysts through controlling the precursorcontent.

Single-Step Production of a TiO2@MoS2 Heterostructure and Its Applications as a Supercapacitor Electrode and Photocatalyst for Reduction of Cr(VI) to Cr(III).

In this study, we have reported a one-step synthesis of a TiO2@MoS2 heterostructure. TiO2@MoS2 was synthesized using a facile and cost-effective method. The as-synthesized TiO2@MoS2 heterostructure was characterized by suitable spectroscopic techniques. The obtained TiO2@MoS2 was utilized as a supercapacitor electrode material. Electrochemical studies show that the TiO2@MoS2 heterostructure possesses a specific capacitance of 337 F/g at a current density of 1 A/g in an aqueous solution. Furthermore, an application as a photocatalyst for the photoreduction of toxic hexavalent chromium was reported for the first time. This heterostructure showed the photoreduction of Cr6+ to Cr3+ in 120 min with formic acid as a scavenger under direct sunlight. A plausible mechanism of photoreduction of Cr6+ to Cr3+ under natural sunlight irradiation using TiO2@MoS2 is proposed.

Facile and eco-friendly synthesis of TiO2 NPs using extracts of Verbascum thapsus plant: an efficient photocatalyst for reduction of Cr(VI) ions in the aqueous solution

In this study, a fast and green synthesis of TiO2 nanoparticles (TiO2 NPs) is investigated using Verbascum thapsus (V. thapsus) plant aqueous extract as a reducing and stabilizing agent at room temperature. The TiO2 NPs formation and the optical properties were followed by the absorption spectra in ultraviolet–visible spectroscopy. This spectrum showed a strong absorption peak of around 356 nm. Moreover, the green synthesized TiO2 NPs were characterized by different techniques, for example, X-ray powder diffraction was used to analyze the phase and crystal structure, Fourier-transform infrared spectroscopy was conducted to know the functional groups involved in the NPs TiO2, and transmission electron microscopy was carried out to determine the morphology and size. The results showed a successful synthesis and anatase phase with spherical shape and smaller than 13 nm and also the presence of a few phytochemicals of the extracts around the synthesized TiO2 NPs, which acted as stabilizing the NPs. X-ray photoelectron spectroscopy analysis was carried out to characterize TiO2 NPs for evaluating the chemical states of the elements. The catalytic activity of the green synthesized TiO2 NPs was examined on photoreduction of Cr(VI) ions in the aqueous solution. The found conditions are as follows: [TiO2 NPs] = 750 mg/L, pH = 3.5, T = 25 °C and after 120 min of reaction photocatalytic reduction of Cr(VI) ions, 79.6% reduction efficacy (RE) was achieved. It was found that the reduction kinetic fitted the pseudo-first-order model. Finally, the photocatalyst reusability was investigated after five times of recovery; RE was reduced to 78.1%.

Synthesis of titanium based hetero MOF photocatalyst for reduction of Cr (VI) from wastewater

Cr (VI) is one of the well-known toxic contaminant coming from leather tanning, metal finishing, textile industries etc. As per world health organization standard, limit for Cr (VI) in drinking water is 0.05 mg/l. In last few years, Metal organic framework (MOFs) based photocatalyst has find great interest for environmental remediation. In this work, titanium based MOFs NH2-MIL-125 and NTU-9 was integrated to make a hetero MOF NTU-9/NH2-MIL-125 (HMF) via refluxing method. It was characterized by XRD, TGA, FE-SEM, FT-IR, XPS, UV–vis (DRS) and PL etc. XRD indicates crystallinity and framework nature of all the synthesized MOFs. Thermal stability of HMF is improved to 520 °C in comparison to NTU-9. Diffuse reflectance spectra exhibit HMF having band gap of 2.2 eV absorbing up to 563 nm. BET surface area of NTU-9, NH2-MIL-125 and HMF were found to be 986, 1267 and 550 m²/g respectively indicating their microporous nature. In order to compare the photocatalytic activity, Cr (VI) solution was chosen a model wastewater. Because of more efficient charge separation, HMF is found to show better activity in comparison to both the contributing MOFs. Acidic condition favors the Cr (VI) reduction and HMF achieves 100% reduction within 90 min of visible light irradiation. In same time NTU-9 and NH2MIL-125 could exhibit only 35 and 55% reduction respectively. This study may give new direction to the study of hetero MOFs for environmental application.

Facile Fabrication of rGO/Rutile TiO2 Nanowires as Photocatalyst for Cr(VI) Reduction

Abstract Reduced Graphene Oxide (rGO) was successfully deposited on TiO2 nanowires (TNWs) via electrophoretic process. The nanowires were produced by thermal oxidation of titanium in the presence of KOH as a catalyst. It was found that the presence of KOH resulted in NWs with length up to 500 nm and average diameter of 50 nm. Nevertheless the distribution of nanowires on Ti foil varied as a function of KOH concentration. The fabricated rGO/TNWs sample was then used as photocatalyst for reduction of Cr(VI) under UV and visible light. It appears that under UV and visible light 100% reduction of 10 mg/L Cr(VI) solution was achieved within 30 and 60 minutes respectively on the rGO/TNWs sample. This could be due to the excess of electrons rGO possessed which aid in the reduction of Cr(VI) to Cr(III) as well as photogenerated electrons in TNWs under UV light.

Activated carbon (prepared from secondary sludge biomass) supported semiconductor zinc oxide nanocomposite photocatalyst for reduction of Cr(VI) under visible light irradiation

Activated carbon prepared from waste tannery sludge biomass was employed in the synthesis of carbon supported ZnO photocatalyst (ZnO-SBAC). Different ratios of ZnO-SBAC (ZC) were synthesized by hydrothermal method. The prepared materials were characterized thoroughly. From the UV–vis-DRS data, zinc: carbon 2:3 ratio (ZC-2:3) was found to have lower band gap energy of 2.96 eV compared to other ratios. FE-SEM analysis revealed the ZnO flakes to lie on the surface of the carbon. The prepared ZC-2:3 nanocomposites has higher surface area of 216.35 m2/g compared to pristine ZnO 11.60 m2/g. The in-situ generation of OH radicals was detected by EPR analysis. The prepared ZC nanocomposite material was employed as a visible active photocatalyst for the reduction of Cr(VI) ions. Among the prepared ratios, ZC-2:3 exhibited the highest activity. The preliminary photocatalytic studies showed acidic medium (pH 2.25) and a catalyst dosage of 10 mg/10 mL to be optimum. The kinetic studies showed the photo reduction of Cr(VI) using pristine (P-ZnO) and ZnO-SBAC to follow pseudo-first order kinetics. The effect of adsorption (dark reaction) was investigated using Langmuir and Freundlich isotherms. ZC has better adsorption capacity (3.54 mg/g) compared to P-ZnO (0.76 mg/g) which may increase the photoreduction of Cr(VI) ions. The ZC-2:3 nanocomposite showed better reusability photocatalyst without affecting its performance up to three cycles when compare to P-ZnO. The prepared ZnO-SBAC exhibits good synergetic effect of adsorption followed by photoreduction for the conversion of Cr(VI) to Cr(III).

Photocatalytic Synthesis of Copper Colloids from Cu(II) by the Ferrihydrite Core of Ferritin

The iron-storage protein ferritin encapsulates a nanoparticle of iron oxide. The size and properties of these nanoparticles can be adjusted by controlled oxidative hydrolysis reactions of Fe(II). This mineralized ferritin protein cage has previously been shown to act as an effective photocatalyst for reduction of Cr(VI). In the present work, we demonstrate that Fe(O)OH-mineralized ferritin catalyzes the photoreduction of Cu(II) to form a stable, air-sensitive, colloidal dispersion of Cu(0). In addition, the particle sizes of the Cu colloids can be controlled by varying the ratio of Cu(II) to ferritin. This illustrates an important principle, namely that the properties of one preformed material can be utilized for the specific synthesis of a second material, thus tailoring the desired physical properties of the final products. This procedure represents a multistep materials synthesis: the formation of a new nanomaterial from a catalytic precursor.