Photocatalytic Reduction Performance Research Articles

Co-doped MoS2 NPs with matched energy band and low overpotential high efficiently convert CO2 to methanol

Co-doped MoS2 NPs (30nm in diameter) was prepared by hydrothermal method and used for photoelectrocatalytic reduction of CO2. Compared with MoS2, the novel catalyst Co-doped MoS2 NPs obtained the valence band and conduction band locating at 0.89V and −0.52V, which leaded to the high efficient photocatalytic reduction performance. In the aspects of electrocatalysis, resistance reduces by 85KΩ, the conductivity of the target material was enhanced greatly, the reduction overpotential for CO2 decreases from −0.82V to −0.64V, which lead to a large improvement on electrocatalytic activity finally. Thus, the Co-doped MoS2 NPs have both excellent photocatalytic performance and excellent electrocatalytic performance. The main CO2 reduction product is methanol, and the yield of which reaches 35mmolL−1 at 350min. The results have guiding significance for the photoelectric catalyst design, which also have theoretical significance for the photoelectrocatalytic reduction of CO2.

Chemically controlled growth of porous CeO2 nanotubes for Cr(VI) photoreduction

A nanowire-directed templating solution-based synthesis strategy was developed to selectively prepare uniform CeO2 nanotubes and heterostructured nanowires by fine-tuning surface chemistry of K1.33Mn8O16 nanowires. The morphology of CeO2 nanotubes and the decorative growth of solid CeO2 particles on K1.33Mn8O16 nanowires changed as the concentration of sodium dodecyl benzene sulfonate (SDBS) was altered. The resultant porous CeO2 nanotubes showed excellent water purification performance for oxalic acid-induced photocatalytic reduction of Cr(VI) under UV light irradiation at room temperature. The enhanced ability for Cr(VI) photoreduction on the obtained CeO2 nanotubes were investigated. Our findings provide a new means to chemically controlled growth of CeO2 nanostructures and demonstrate a highly robust and potential material for the purification of Cr(VI) polluted water.

One-step in-situ hydrothermal synthesis of SnS2/reduced graphene oxide nanocomposites with high performance in visible light-driven photocatalytic reduction of aqueous Cr(VI)

Photocatalytic reduction of aqueous Cr(VI) was successfully achieved on SnS2/reduced graphene oxide (SnS2/RGO) nanocomposites. The SnS2/RGO nanocomposites have been synthesized via facile in situ hydrothermal reactions of SnCl4·5H2O, thiourea (NH2CSNH2), and graphene oxide nanosheets without any modified reagents. The physical and chemical properties of SnS2/RGO were studied by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectra, and UV–vis diffuse reflectance spectra. The photocatalytic reduction of aqueous Cr(VI) by SnS2/RGO nanocomposites was evaluated at ambient temperature under visible light (λ > 420 nm) irradiation. The SnS2/RGO nanocomposites exhibit excellent reduction efficiency of Cr(VI) (~90 %) than that of pure SnS2.

Microwave-assisted synthesis of hematite/activated graphene composites with superior performance for photocatalytic reduction of Cr(vi)

α-Fe2O3/aMEGO composites are demonstrated to be excellent photocatalysts in Cr(vi) reduction.

Photocatalytic reduction of Cr(vi) by polyoxometalates/TiO2electrospun nanofiber composites

Polyoxometalates (Ti0.75PW12O40, Ti-PTA)/TiO2 nanofiber composites were fabricated by a simple electrospinning technique and then high temperature calcination. In the structure, Ti-PTA, as an electron relay, can accept the photo-generated electrons from the conduction band of TiO2, which promote the separation of photo-generated charges in TiO2. Then the electrons stored on Ti-PTA further transfer to the Cr(VI) in the solution to realize the removal of Cr(VI). The Ti-PTA/TiO2 nanofiber composites exhibit enhanced photocatalytic performance for photocatalytic reduction of Cr(VI), which might be a potential photocatalyst for Cr(VI) removal in environmental therapy.

Visible-light CO2 photocatalytic reduction performance of ball-flower-like Bi2WO6 synthesized without organic precursor: Effect of post-calcination and water vapor

• Photocatalytic CO 2 reduction on non-organic synthesized PB-Bi 2 WO 6 was investigated. • CO was detected as the major product. • Increased amount of CO was yielded in the condition with little water vapor. • Photocatalytic performance was enhanced with Bi 2 WO 6 after 550 °C post-annealing. • Renewing the catalysts used in CO 2 photoreduction by water washing was achieved. Nanoplates-composed ball-flower-like Bi 2 WO 6 (PB-Bi 2 WO 6 ) was synthesized by a hydrothermal method without any organic precursor and its performance in photocatalytic reduction of CO 2 was investigated in a continuous-flow reaction system under visible light irradiation (420 nm < λ < 620 nm). CO was detected as the main product of this photocatalytic process and H 2 O was found to suppress the conversion of CO 2 to CO due to its competitive absorption with CO 2 on the medium strength basic sites of Bi 2 WO 6 . PB-Bi 2 WO 6 annealed at 550 °C showed superior CO yield in the condition with little water vapor. It might be attributed to the enhanced crystallinity, significantly decreased recombination rate of photo-generated electrons and holes and more stable basic sites for strengthened CO 2 adsorption, according to characterization results by XRD, SEM, UV–vis SRS, PL and CO 2 -TPD. However, comparing with PB-Bi 2 WO 6 , the negative effect of H 2 O was even more prominent on the annealed sample because of the reduced surface area. Yield decrease was observed during the irradiation time due to the adsorption of intermediates generated but fortunately washing with deionized water was found to be an effective way to renew the catalyst.

Synergistic Photoelectrochemical Synthesis of Formate from CO2 on {121̅} Hierarchical Co3O4

To propel the thermodynamically unfavorable conversion of greenhouse CO2 to renewable fuel with remarkable efficacy, we here proposed a visible-light-driven synergistic photoelectrochemical (PEC) synthesis of formate from CO2. Formate was the only C1 product photoelectrochemically generated on the fabricated hierarchical Co3O4 electrode. Results showed that up to 384.8 ± 7.4 μmol of formate was produced within 8 h owing to the synergistic PEC reduction process. This enhanced production of formate, outnumbering most of the reported work, was further found to be indispensable of the superior photocatalytic and electrocatalytic reduction performance of the as-prepared electrode. Research further elucidated that the photocatalytic activity was intimately related with the hierarchical Co3O4 microstructure, in which a single-crystalline microflower was interconnected by thin nanopetals on one-dimensional rhombus nanorod. Additionally, the construction of {121} facet allowed high Co3+ exposure on Co3O4 surface,...

Visible light photocatalytic reduction of Cr(VI) on Ag3PO4nanoparticles

AbstractAg3PO4 nanoparticles of ∼300 nm were synthesized by an ion-exchange reaction between AgNO3 and (NH4)2HPO4 at ambient condition. X-ray powder diffraction, scanning electron microscopy, UV−Vis diffuse reflectance spectroscopy were employed to investigate the phase structure, morphology, and optical property of the Ag3PO4 nanoparticles. Nearly 80% of Cr(VI) ions was removed after visible-light irradiation in Ag3PO4 suspension, the excellent photocatalytic reduction performance due to the high separation efficiency of electron and hole pairs. In addition, the possible photoreduction mechanism of Cr(VI) in Ag3PO4 suspension was discussed. The system of Ag3PO4 may provide an alternative way for the efficient removal of Cr(VI) under visible-light irradiation.

On sol–gel derived Au-enriched TiO2 and TiO2-ZrO2 photocatalysts and their investigation in photocatalytic reduction of carbon dioxide

Gold-enriched TiO2 and TiO2-ZrO2 and their parent counterparts were prepared by using the sol–gel process controlled within the reverse micelles environment, followed by impregnation in AuCl3 solution. Catalysts were characterized by organic elementary analysis (OEA), inductively coupled plasma mass spectrometry (ICP MS), N2 physisorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) combined with electron diffraction, UV–vis spectroscopy, and tested in CO2 photocatalytic reduction. The performance of photocatalysts iluminated by UV-lamp with the wavelenght maximum at 254nm was decreasing in the order TiO2-ZrO2>Au/TiO2-ZrO2>TiO2>Au/TiO2>TiO2 Evonic P25. The photocatalytic performance decrease over Au/TiO2-ZrO2 and Au/TiO2, compared to their parent counterparts, can be explained by the presence of too large Au particles, which block the oxide surface and either reduce the light absorption capability of the catalysts, or serve as the recombination centres. Higher photocatalytic performance of the amorphous TiO2-ZrO2 than of the nanocrystalline TiO2 can be ascribed to the enlarged surface area and higher photoactivity of titania-zirconia oxide mixture under the UV lamp with the wavelenght maximum at 254nm. With regard to crystalline materials the appropriate anatase crystallite-size plays a key role in performance of CO2 photocatalytic reduction. Moreover, correlation between the adsorption edge and the anatase crystallite-size was revealed.

Photocatalytic reduction of Cr(VI) with TiO2 film under visible light

The performance of photocatalytic reduction of chromium (VI) via a new TiO2 film and a platinum anode was systematically evaluated. The as-prepared TiO2 film is composed of a dye-sensitized zone and a catalysis zone. Charge separation was accomplished with electron transferring to the catalysis zone and positive charge transforming to an anode. A powerful reduction ability of the reaction system was achieved in the absence of any organics under visible light irradiation. Several parameters including pH, dissolved O2, the primary active species, the durability of the as-synthetized film and so on were investigated.

Honeycomb Cupric Oxide and Hematite Nanotubes Synergism Photoelectro-reduction CO2

Vertically aligned Fe2O3 nanotubes (Fe2O3 NTs) arrays were prepared on the iron foil by potentiostatic anodization method. The anodization experiments were performed under 30 V for 2 h (20 degrees C). The ferrous foil was working electrode and titanium foil was counter electrode. The electrolytes were consisted of 0.25 wt% NH4F in an aqueous solution (Volume of water : glycol=3 : 97). After sonicating for 5 min, the samples were put under oxygen atmosphere with the flow rate of 60 sccm (standard cubic centimeters/min) and heated to 500 degrees C with the rate of 3 degrees C.min(-1) and maintained at 500 degrees C for 2 h. Then cooled to room temperature with the rate of 3 degrees C.min(-1). Honeycomb structure cupric oxide (CuO HCs) were decorated on the surface of Fe2O3 NTs by the pulse electrochemical deposition method. This was done by CHI660D potentiostat in 1 mol.L-1 CuSO4 solution (40 degrees C) in a three-electrode configuration. The Fe2O3 NTs electrode worked as counter electrode, Hg/Hg2Cl2 in saturated KCl solution as reference electrode, and platinum wire as working electrode, respectively. A 10 ms cathodic pulse with a current density of -70 mA.cm(-2) was employed. After that followed by a 1 ms anodic pulse and its density was +70 mA.cm(-2) to prevent damage of the Fe2O3 NTs structure. Finally was a 1000 ms rest time. The electrodeposition time was 36 s, with a forward duty cycle of 0.99% (considering cathodic, anodic and rest components). Then the samples were annealed under oxygen atmosphere with the flow rate of 60 sccm then heated to 300 degrees C with the rate of 3 degrees C.min(-1) and maintained at 300 degrees C for 2 h. Then cooled to room temperature with the rate of 3 degrees C.min(-1). Then the CuO HCs/Fe2O3 NTs catalysis was obtained. The SEM images showed that CuO HCs distributed uniformly on the surface of Fe2O3 NTs that arranged in order were volcano-like. Measured by UV-vis DRS (ultraviolet-visible diffuse reflection spectrum) and valence band photoemission spectrum, its band energy has been narrowed from 2.03 eV to 1.84 eV after CuO decorating. It also has admirable photocatalytic and electrocatalytic reduction performance. The main product of photoelectrocatalytic CO2 reduction identified by chromatography was methanol and its concentration reached 3.77 mmol/L after 6 h. The study has some guidance and reference significance for photoelectrocatalytic CO2 reduction.

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.

Ultrathin, Single-Crystal WO3 Nanosheets by Two-Dimensional Oriented Attachment toward Enhanced Photocatalystic Reduction of CO2 into Hydrocarbon Fuels under Visible Light

An ultrathin, single-crystal WO3 nanosheet of ∼4-5 nm in thickness, corresponding to six repeating unit cells of monoclinic WO3 along the c axis, was synthesized with laterally oriented attachment of tiny WO3 nanocrystals formed using a solid-liquid phase arc discharge route in an aqueous solution. Size-quantization effects in this ultrathin nanostructure alter the WO3 band gap to enable the nanosheet to exhibit enhanced performance for photocatalytic reduction of CO2 in the presence of water in hydrocarbon fuels that do not exist in its bulk form.

One-step in situ solvothermal synthesis of SnS2/TiO2 nanocomposites with high performance in visible light-driven photocatalytic reduction of aqueous Cr(VI)

SnS2/TiO2 nanocomposites with adjustable TiO2 contents were synthesized directly via the solvothermal reactions of SnCl4·5H2O, thioacetamide and different amounts of tetrabutyl titanate in the mixed solvents of ethanol and acetic acid at 180°C for 12h. The structures, compositions, Brunauer–Emmett–Teller (BET) specific surface areas and optical properties of the as-synthesized products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, N2 adsorption and UV–vis diffuse reflectance spectra, and their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (λ>420nm) irradiation. Furthermore, contrast photocatalytic experiments were also conducted for different doses of the as-synthesized SnS2/TiO2 nanocomposite, SnS2 and physical mixture of SnS2 and TiO2. It was found that the as-synthesized SnS2/TiO2 nanocomposite with a suitable TiO2 content (e.g., 44.5mass% TiO2) not only exhibited extraordinary superior photocatalytic activity to SnS2, TiO2 and physical mixture of SnS2 and TiO2 (44.5mass%) at different catalyst doses, but also had good photocatalytic stability. Moreover, Cr(VI) can be reduced to Cr(III) by SnS2/TiO2-mediated photocatalysis. The tight heterojunction structure of the as-synthesized SnS2/TiO2 nanocomposite, which can facilitate interfacial electron transfer and reduce the separation and self-agglomeration of two components, was considered to play an important role in achieving its greatly improved photocatalytic performance.

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.

Size-Tunable Hydrothermal Synthesis of SnS2 Nanocrystals with High Performance in Visible Light-Driven Photocatalytic Reduction of Aqueous Cr(VI)

SnS(2) nanocrystals with adjustable sizes were synthesized via a hydrothermal method from the aqueous solution of common and inexpensive SnCl(4)·5H(2)O, thioacetamide and citric acid, simply by varying the reaction temperature and reaction time. The structures, Brunauer-Emmett-Teller (BET) specific surface areas and optical properties of the resultant SnS(2) nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, N(2) adsorption/desorption isotherms, and UV-vis diffuse reflectance spectra. Besides, their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (λ > 420 nm) irradiation. It was found that the photocatalytic activities of SnS(2) nanocrystals in aqueous suspension depended on their synthesis conditions. The product synthesized under suitable hydrothermal conditions (for example, at 150 °C for 12 h) not only showed high visible light-driven photocatalytic activity in the reduction of aqueous Cr(VI), but also showed good photocatalytic stability. Our photocatalytic results suggested that SnS(2) nanocrystals are a promising photocatalyst in the efficient utilization of solar energy for the treatment of Cr(VI)-containing wastewater.

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.

Synergistic Effect of N and Ni2+ on Nanotitania in Photocatalytic Reduction of CO2

Nitrogen and nickel codoped nanotitania ( N-Ni/TiO2) photocatalysts for producing methanol by photocatalytic reduction of CO2 were prepared by an improved sol-gol method. The catalysts were characterized by XRD, HRTEM, DES, FTIR, TG-DSC, and UV-Vis, respectively. The experimental results indicated that nano- N-Ni/TiO2 had better properties than the pure nanotitania ( TiO2), N doped titania ( N/TiO2), and Ni2+ doped titania ( Ni/TiO2), considering their performance of photoresponse and photocatalytic reduction of CO2. The methanol yield could reach 482.0μmol/g-cat under optimal conditions. Additionally, the synergetic effect of N and Ni2+ on nano- TiO2 in photocatalytic reduction of CO2 was explained, and the mechanism of photocatalytic reduction CO2 on N-Ni/TiO2 catalyst was proposed.