Graphene Oxide Photocatalysts Research Articles

Fabrication of Fe/BiOCl/RGO with enhanced photocatalytic degradation of ciprofloxacin under visible light irradiation

The Fe-doped BiOCl/reduced graphene oxide (Fe/BiOCl/RGO) photocatalyst was synthesized for ciprofloxacin (CIP) degradation under visible light irradiation via a facile and controllable solvothermal approach. Fe-doping and RGO incorporated greatly inhibit the agglomeration of BiOCl and significantly enhance the photodegradation activity by facilitating the separation of photogenerated electron-hole pairs, which could almost completely degrade CIP solution in 180 min. Moreover, Fe/BiOCl/RGO reaches the highest rate constant of 0.021 min−1, which is 2.1 and 4.4 times larger than those of Fe/BiOCl and BiOCl, respectively. Besides, Fe/BiOCl/RGO exhibits excellent stability, which can remain ∼90% after five cycling degradation. Photogenerated ·OH and h+ for CIP degradation are confirmed as the main active species through free radical capture experiments. The improved photocatalytic activity of Fe/BiOCl/RGO is attributed to the strong synergistic effect of Fe-doping and RGO addition, which efficiently extends the visible light absorption extent, along with accelerating the separation and conversion of photogenerated electrons and holes, thus promoting the utilization of photocatalysts under visible light irradiation.

Fabrication of BiVO4/ reduced graphene oxide photocatlyst for hexavalent chromium reduction under visible region

Bismuth vanadate (BiVO4) is widely used as a visible light photocatalyst for elimination of organic and inorganic pollutants in aqueous solution. An integration with few layer graphene oxide into BiVO4, significantly enhance the photocatalytic activity in the visible region due to it’s high charge transport and separation. Herein, we have designed BiVO4 on reduced graphene oxide (rGO) photocatalyst synthesised via simple solution phase method. BiVO4 nanocrystals nanoplates were fabricated using bismuth (III) nitrate, ammonium metavanadate with ammonium hydroxide, and polyethylene glycol as a stabilising agent. The resulting photocatalytic catalyst showed an excellent activity towards Cr(VI) removal (as a model inorganic pollutant) under visible light, which is evidenced with photoelectrochemical studies. The photocatalytic performance for Cr(VI) removal rates over BiVO4/rGO showed much higher activity than BiVO4 in visible light. Furthermore, the catalyst efficiency was confirmed through photoelectrochemical, and optoelectronic properties.

Insight into a novel microwave-assisted W doped BiVO4 self-assembled sphere with rich oxygen vacancies oriented on rGO (W-BiVO4-x/rGO) photocatalyst for efficient contaminants removal

A novel W doped BiVO4 with rich oxygen vacancies (OVs) oriented on reduced graphene oxide (rGO) photocatalyst (W-BiVO4-x/rGO) was developed by a simple one-step microwave hydrothermal method for efficient removal of ciprofloxacin (CIP) and chlortetracycline (CTC) under visible light. The synergistic effect of W doping, BiVO4 with OVs, and rGO on the enhancement of photocatalytic activity was clarified from experimental and Density Functional Theory (DFT) calculations results. W doping significantly improved the density of photo-generated charge carriers. The introduction of rGO enlarged the specific surface area, expanded the light absorption range, and promoted the charge transfer of BiVO4. OVs both narrowed the band gap and enhanced the generation of O2−. W doping and OVs both enhanced the interactions between BiVO4 and rGO. The CIP degradation rate constant of W-BiVO4-x/rGO photocatalyst was 1.73, 5.32, 6.43, and 10.70 times higher than those of W-BiVO4/rGO, BiVO4/rGO, W-BiVO4, and BiVO4, respectively. Besides, W-BiVO4-x/rGO photocatalyst prepared by microwave hydrothermal method exhibited higher photocatalytic activity and better combination between materials. This study offers a new strategy to address the problem of antibiotic residues in wastewater.

Influence of rGO and Preparation Method on the Physicochemical and Photocatalytic Properties of TiO2/Reduced Graphene Oxide Photocatalysts

In this study, a series of TiO2/rGO photocatalysts were obtained with a two-step procedure: a solvothermal method and calcination at 300–900 °C in an argon atmosphere. It was noted that the presence of rGO in photocatalysts had an important role in the changes in crystallite size and specific surface area. In TiO2/rGO samples, different surface functional groups, such as C−Cgraph, C−Caliph, C−OH, C=O, and CO(O), were found. It was observed that rGO modification suppressed the anatase-to-rutile phase transformation. The photocatalytic activity of the obtained nanomaterials was investigated through the decomposition of methylene blue under UV and artificial solar light irradiation. It was found that the adsorption degree played an important role in methylene blue decomposition. The experimental results revealed that TiO2/rGO samples exhibited superior removal efficiency after calcination for methylene blue compared toTiO2 without rGO, as well as a commercial photocatalyst KRONOClean 7000. It was noted that photocatalytic activity increased with the increase in the calcination temperature. The highest activity was observed for the sample calcined at 700 °C, which consisted of 76% anatase and 24% rutile. This study clearly demonstrated that TiO2/rGO samples calcined in argon can be used as efficient photocatalysts for the application of methylene blue decomposition.

Photo-Fenton interfacial phenomena on graphene oxide: Computational and experimental investigations

For optimum photocatalytic efficiency, besides appropriate band positions, the molecules to be reduced should adsorb on the nucleophilic sites, and those to be oxidized should effectively interact with the electrophilic sites of a photo-excited photocatalyst. The present research investigates the photocatalytic properties of graphene oxide (GO) materials from this novel perspective. We combine density functional theory (DFT) calculations, large-scale classical molecular dynamics (MD), and experimental studies for comprehending the Fenton (in the dark) and visible light photo-Fenton catalytic activities of two GO materials for orange-G (OG) dye degradation. DFT and time-dependent density functional theory (TD-DFT) calculations located a GO model's nucleophilic and electrophilic functionalities in the ground and photo-excited states. Then large-scale classical MD simulations in an aqueous medium gave information about how different reactants interact with varying oxygen functionalities on the GO structure. The photo-Fenton activities of two GO samples with different visible range bandgaps were experimentally evaluated for OG degradation along with these computational studies. The GO photocatalysts efficiently degraded the target dye. Finally, the experimental and computational results are combined to shed light on critical aspects of heterogeneous Fenton and photo-Fenton interfacial phenomena operating on a typical GO structure.

Optimization of TiO2 immobilized – Reduce graphene oxide photocatalyst toward organic compounds in aqueous medium

In this work, a one-pot hydrothermal route was synergistically applied for TiO2 immobilized reduced graphene oxide (TiO2/rGO) facilitation. The material was characterized by modern analysis methods and studied the photocatalytic performance with methylene blue (MB) in the water. The characteristic results expressed that TiO2 in truncated octahedral bipyramidal structure with 4–25 nm was disseminated onto the rGO base. Simultaneous effects of the reaction temperature, pH, adsorption time, photocatalytic time, MB concentration, and catalyst dosage on the MB photodegradation of TiO2/rGO were also conducted by full factorial experimental design according to Placket–Burman and Box–Behnken designs. At room temperature, after 2h–adsorption and photodegradation with MB concentration of 23 mg/L in pH of 10 solution and 20 mg catalyst, nearly 100% of MB was productively decomposed out of the medium with a relatively high reaction rate constant. The photocatalytic performance showed an excellent impact toward other types of organic contaminants with the above condition, indeed affirming an extensive use in wastewater treatment with organic pollutants.

Multichannel Electron Transmission and Fluorescence Resonance Energy Transfer in In2S3/Au/rGO Composite for CO2 Photoreduction.

Efficient electron transmission is an important step in the process of CO2 photoreduction. In this paper, a multi-interface-contacted In2S3/Au/reduced graphene oxide (rGO) photocatalyst with the fluorescence resonance energy transfer (FRET) mechanism has been successfully prepared by the solvothermal, self-assembly, and hydrothermal reduction processes. Photocatalytic CO2 reduction experiments showed that the In2S3/Au/rGO (IAr-3) composite exhibited excellent photoreduction performance and photocatalytic stability. The yields of CO and CH4 obtained after the photoreduction process with IAr-3 as the catalyst were around 4 and 6 times higher than those of pure In2S3, respectively. Photoelectrochemical analysis showed that the multi-interface contact and FRET mechanism greatly improved the generation, transmission, and separation efficiency of carriers photogenerated within the photocatalyst. In situ FTIR test was applied to analyze the photocatalytic CO2 reduction process. 13C isotope tracer test confirmed that the carbon source of CO and CH4 was the CO2 molecules in the photoreduction process rather than the decomposition of catalyst or TEOA. A potential enhanced photocatalytic mechanism has been discussed in total.

Constructed Z-Scheme g-C3N4/Ag3VO4/rGO Photocatalysts with Multi-interfacial Electron-Transfer Paths for High Photoreduction of CO2.

Z-scheme g-C3N4/Ag3VO4/reduced graphene oxide (rGO) photocatalysts with multi-interfacial electron-transfer paths enhancing CO2 photoreduction under UV-vis light irradiation were successfully prepared by a hydrothermal process. Transmission electron microscope images displayed that the prepared photocatalysts have a unique 2D-0D-2D ternary sandwich structure. Photoelectrochemical characterizations including TPR, electrochemical impedance spectroscopy, photoluminescence, and linear sweep voltammetry explained that the multi-interfacial structure effectively improved the separation and transmission capabilities of photogenerated carriers. Electron spin resonance spectroscopy and band position analysis proved that the electron-transfer mode of g-C3N4/Ag3VO4 meets the Z-scheme mechanism. The introduction of rGO provided more electron-transfer paths for the photocatalysts and enhanced the stability of Ag-based semiconductors. In addition, the π-π conjugation effect between g-C3N4 and rGO further improved the generation and separation efficiency of photogenerated electron-hole pairs. Then, the multiple channels (Ag3VO4 → CN, Ag3VO4 → rGO → CN, and rGO → CN) due to the 2D-0D-2D structure greatly improving the photocatalytic CO2 reduction ability have been discussed in detail.

Hydrothermal preparation of novel rGO-KTaO3 nanocubes with enhanced visible light photocatalytic activity

In this study, nanocubes KTaO3–reduced graphene oxide (rGO–KTaO3) photocatalysts were synthesized by a facile hydrothermal method. Different technical methods were carried out to characterize the as-prepared compounds. UV–Vis spectra show that the absorption sideband of the complexes red-shift to visible light region, which enhances the light utilization. Meanwhile, X-ray photoelectron spectroscopy (XPS) reveals that the graphene oxide (GO) in the composite has been partially reduced, leading to more effective electron transport and thus improving the photocatalytic efficiency. Furthermore, photocatalytic degradation efficiency of Methylene blue (MB) and Rhodamine B (RhB) in the presence of rGO–KTaO3 reaches 96% and 98%, which is 10 times of that of KTaO3. The synthesized rGO-KTaO3 has good photocatalytic properties. Moreover, the stability of this photocatalyst is particularly excellent. The detailed mechanism of photocatalysis has been carefully discussed in the article.

Microbial synthesis of Cu7S4/rGO nanocomposites with efficient photocatalytic activity for the degradation of methyl green

Cu7S4/reduced graphene oxide (rGO) photocatalysts are attracting increasing interest because of their low cost and environmental friendliness.

Hydrothermal preparation of B–TiO2-graphene oxide ternary nanocomposite, characterization and photocatalytic degradation of bisphenol A under simulated solar irradiation

Boron-doped TiO2 decorated on graphene oxide photocatalysts (denoted as GO@B–TiO2) were prepared for the effective photocatalytic treatment of bisphenol A (BPA) from water under simulated solar light. To prepare GO@B–TiO2 nanocomposites, B–TiO2 was initially synthesized via a sol-gel procedure and subsequently decorated on graphene oxide at 70 °C, by a facile hydrothermal method. Characterization results show that B–TiO2 particles are anchored on the surface of graphene oxide successfully. Their photocatalytic efficiency could also be adjusted by changing the ratios between B–TiO2 and GO. The optimum GO loading is 2 wt%, at which GO@B–TiO2 nanocomposite photocatalyst could achieve the best BPA degradation percentage of 47.66% compared with B–TiO2 materials (18.78%) after 240 min of solar irradiation. The dominant reactive oxygen species (ROS) formed during the photocatalytic abatement of BPA were determined to be O2.- and .OH. The presence of carbonate and chloride induced moderate inhibitory effect on GO@B–TiO2 (2 wt% GO), while bicarbonate and nitrate displayed only minor effect towards photocatalytic degradation of BPA. Based on these results, the as-prepared nanocomposites may be used as efficient and promising photocatalysts in secondary treatments to degrade recalcitrant contaminants in water exploiting the visible-light region of the full solar spectrum.

Fabrication of non-covalently grafted Cu(acac)2 over two-dimensional graphene oxide nanosheets: An environmentally benign noble photocatalyst for visible-light-driven degradation of phenol

Herein, we report the development of a novel recyclable sonochemical non-covalent grafting of Cu(acac)2 over two-dimensional graphene oxide (GO) photocatalyst degrades phenol under visible light irradiation. The photocatalyst was prepared and characterized by XRD, FTIR, SEM, HR-TEM, EDAX, XPS, BET. The results of the analysis suggest the uniform grafting of Cu(acac)2 over the surface of GO. The photodegradation efficiency of GO/Cu(acac)2 was performed both under light and dark. The composite showed up to 90% degradation of phenol in 90 min when irradiated under the visible light. This improved photocatalytic activity may be attributed to the reduction in the band gap of pristine GO owing to the grafting of Cu(acac)2. The Langmuir-Hishelwood pseudo-first-order kinetic model of the degradation was performed and the rate constant (k) in presence of light for the composite was found to be 9.94 × 10−4 min−1 which is almost three times than the rate constant measured in presence of light with pristine GO.

Outstanding photocatalytic activity of CoFe2O4 /rGO nanocomposite in degradation of organic dyes

Abstract In this research, the efficiency of organic dyes degradation over cobalt ferrite, CoFe2O4, nanoparticles loaded on the reduced graphene oxide (rGO) photocatalyst was investigated. The effect of Triton X-100 (TX-100) surfactant usage in synthesis process was also studied. The addition of rGO to the CoFe2O4 and use of TX-100 led to a decrease in crystallite size to 14 nm, increase of specific surface area to 116 m2/g and decrease of band gap energy to 1.75 eV. Vibrating sample magnetometer (VSM) study displayed the reduction of magnetic properties in CoFe2O4/rGO nanocomposite, while the coercivity increased sharply when the TX-100 used as a surfactant. Reduction in Photoluminescence (PL) peaks, increasing average lifetime (~1.92 ns) obtained from time-resolved fluorescence (TRF), increasing the photocurrent value and the reduction of charge transfer resistance confirmed that the CoFe2O4/rGO nanocomposite with TX-100 surfactant have a better charge transfer efficiency comparing with other samples. 5 ppm of initial methylene blue (MB) concentration, and 0.5 g/L of catalyst dosage was determined as the optimal photocatalyst operating setting after 180 min of visible light irradiation. The nanocomposite sample showed the higher degradation efficiency for MB than those of methyl orange (MO) and Rhodamine B (RhB) dyes under visible light illumination. Also, the kinetics and mechanism of photocatalytic degradation process were explained in detail. The magnetically recyclable nanocomposite exhibited high reusability and stability during the cyclic photocatalytic degradation.

Evaluation of TiO2 and SnO Supported on Graphene Oxide (TiO2-GO and SnO-GO) Photocatalysts for Treatment of Hospital Wastewater

The effectiveness of two photocatalysts, TiO2 and SnO, supported on graphene oxide (TiO2-GO and SnO-GO) on the removal of organic matter from hospital wastewater effluent was evaluated at laboratory scale. The results of the experimental design allow us to conclude that variables such as catalyst type and catalyst concentration have a significant effect on the organic matter removal efficiency of the photocatalytic process. The highest levels of removal efficiencies—for chemical oxygen demand, 85%, for phenols, 80%, and for dissolved organic carbon, 94%—were achieved using a TiO2-GO catalyst with a concentration in the wastewater of 1.5 g/L.

Multi-color Reversible Photochromisms via Tunable Light-Dependent Responses

Summary Reversible multi-color chromic systems are critical for the development of advanced sensors, encryption devices, and rewritable media. While many systems show chromic responses to applied stimuli, few show distinct multi-colored states within the same system and exhibit limited flexibility in manipulation of the stimuli source. Light-responsive materials have shown promise because of high precision and controllable parameters of the incident light but suffer from slow kinetics limiting the versatility of the photochromic systems. Here, we report a highly active oxygen vacant titanium oxide/reduced graphene oxide photocatalyst that significantly accelerates the color switching of commercial redox dyes. With the improved catalyst, four photochromic devices are realized: (1) multi-wavelength photochromism, (2) intensity-dependent photochromism, (3) time-dependent photochromism, and (4) dual-response hydro-/photochromism. These devices are based on manipulating the interactions between the light and semiconductor and exhibit a broad range of photochromic behaviors with multi-color states and high reversibility.

Design of novel structured Au/g-C3N4nanosheet/reduced graphene oxide nanocomposites for enhanced visible light photocatalytic activities

In order to surmount the intrinsic disadvantages of raw g-C3N4, we demonstrate simple thermal oxidation exfoliation and facilein situphotoreduction methods to fabricate Au/g-C3N4nanosheet/reduced graphene oxide (Au/CNNS/rGO) photocatalysts.

Atomic-scale synthesis of nanoporous gallium-zinc oxynitride-reduced graphene oxide photocatalyst with tailored carrier transport mechanism.

Surface modified gallium–zinc oxynitride solid solution exhibited outstanding stability and visible-light activity for water splitting. However, the considerable rate of photo-induced charge recombination and the low surface area of the bulk photocatalyst limited its performance. Here, an efficient technique is proposed for the synthesis of a nanoporous oxynitride photocatalyst and its graphene-hybridized material. The nanoporous oxynitride photocatalyst was prepared via a nanoscale solid-state route, using microwave irradiation as an intermolecular-state activation method, Ga3+/Zn2+ layered double hydroxide as an atomic-level uniform mixed-metal precursor, and urea as a non-toxic ammonolysis soft-template. The graphene-hybridized photocatalyst was fabricated using a facile electrostatic self-assembly technique. The photocatalytic activity of the synthesized graphene hybridized nanoporous oxynitride photocatalyst was systematically improved through shortening the majority-carrier diffusion length and enhancing the density of active hydrogen evolution sites within the quasi-three-dimensional nanostructure, reaching 7.5-fold sacrificial photocatalytic hydrogen evolution, compared to the conventional 1 wt% Rh-loaded oxynitride photocatalyst.

Highly efficient Zr-MOF@WO3/graphene oxide photocatalyst: Synthesis, characterization and photodegradation of tetracycline and malathion

In this study, for the first time, a novel MOF based nanocomposite, UiO-66@ WO3/graphene oxide (UiO-66@WG) was synthesized by a solvothermal method and its ability was evaluated for photodegradation of two pollutant models containing aromatic (tetracycline (TC)) and nonaromatic (malathion (MA)). The characterization of nanocomposite was performed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and N2 adsorption–desorption technique. The best efficiencies (84% and 100% for TC and MA respectively) obtained using UiO-66@35WG under 70 min visible light irradiation which is noticeably more efficient when compared with pure UiO-66. This enhancement arises from several aspects containing increase in visible light response, proper matching of conductive and valence bands belong to UiO-66 and WO3 that led to improved separation of electron-hole pair and faster transfer of photoinduced carriers on layers of graphene oxide. The reduced band gap, various functional groups and good availability of active sites also are other positive factors in this design. The total oxygen carbon (TOC) analysis indicated 75%, 83% mineralization efficiency for TC and MA respectively, indicating acceptable decomposition of these pollutants under optimum condition. Furthermore, this nanocomposite shown good reusability after 4 consecutive runs.

Ultrasonic-microwave assisted synthesis of GO/g-C3N4 composites for efficient photocatalytic H2 evolution

There has been increasing interest in the study of photocatalysis technology application in hydrogen production by splitting water because of environmental pollution and energy utilization. In this study, a high efficiency of the photocatalytic H2 production was achieved via graphene oxide (GO) and graphitic carbon nitride (g-C3N4) composite photocatalysts (GO/g-C3N4). The GO/g-C3N4 photocatalysts possessed enhanced activities for hydrogen production than pure g-C3N4 under visible light irradiation. The structural and optical properties of all the synthesized photocatalysts were successfully characterized by XRD, FTIR, XPS, UV–vis spectra, TEM, SEM, N2 adsorption-desorption and photoluminescence spectra techniques. Experimental results indicated that GO/g-C3N4 photocatalysts can reach a high H2-production rate of 224.6 μmol/h (nearly 12 times of that obtained from pure g-C3N4) at GO content of 0.5 wt % and Pt 1 wt % under visible light irradiation. The enhanced photocatalytic activity of GO/g-C3N4 is ascribed to the ability of GO in accepting and transporting electrons from excited g-C3N4, which promotes the charge separation. This work highlights that the affordable and abundant carbon material can be a good candidate for an electron attracting collector and transporter to efficiently lengthen the lifetime of the photogenerated charge carriers in the field of photocatalytic hydrogen production.

Biomineralization of Quantum Confined Nanocrystals and Heterostructures for Electrochemical Applications

Functional nanomaterials are at the core of many innovations in renewable energy generation and catalysis. However, many of these materials are currently synthesized through high temperature, multi-step processes that utilize organic solvents and expensive precursors. These factors increase the complexity and economic and environmental costs of manufacturing scale-up. In contrast, biomineralization, the process by which biological systems produce structural nanomaterials, occurs under ambient conditions in aqueous media utilizing readily available precursors. We have developed a novel single enzyme route for the direct, scalable and controlled synthesis of a variety of pure and hetero-structured metal chalcogenide quantum dots. This approach represents perhaps the simplest biosynthesis system for these materials, consisting of only the single enzyme, a metal precursor, and amino acid sulfur source, and capping agent in an ambient temperature, buffered, aqueous solution. However, tight control of the growth parameters yields size and composition controlled crystalline materials and heterostructures with functional properties comparable to materials synthesized by traditional chemical routes. We demonstrate the application of this approach to direct biomineralization of quantum dots within solar cell photoanodes, and in fully biomineralized quantum dot/reduced graphene oxide photocatalysts.