High Photoactivity Research Articles

Novel metal-free intercalation of g-C3N4 using hyperbranched copolymer for efficient photocatalytic degradation of tetracycline

Herein, graphitic carbon nitride (g-C3N4) structure was successfully intercalated with a hyperbranched copolymer (poly(DEAEMA-co-MMA)) to utilize a novel and applicable photocatalyst (PCN) for antibiotic degradation under visible light illumination. The as-synthesized catalysts were systematically characterized by XPS, FTIR, TEM, XRD, BET, DRS, PL and EIS methods. The intercalation of g-C3N4 with copolymer increased the specific surface area from 46.8 to 210.2 m2/g, leading to increased active sites on the catalyst surface. DRS, PL, EIS techniques and the transient photocurrent responses demonstrated enhanced visible-light absorption and separation efficiency of photo-generated electron-holes for PCN catalyst. XPS analysis revealed the formation of new delocalization π bonds which improves the electronic conductivity. The photocatalytic performance on tetracycline (TC) degradation on PCN catalyst was investigated under visible light irradiation. The intercalated g-C3N4 exhibited much higher photoactivity toward TC degradation (90 %) comparing with bare g-C3N4 (65 %). The enhanced photocatalytic performance of PCN catalyst was mainly assigned to the increased surface area and low recombination rate of the photogenerated charge carriers. Furthermore, the degradation was greatly influenced in the presence of scavengers, suggesting the crucial role of O2− radicals on the performance. The photoactivity was strongly affected by water matrix, which the degradation efficiency altered with high concentrations of anions. In addition, reusability tests revealed that the catalyst was stable until fifth cycle. This work provides a new insight for intercalation of the photocatalyst using a hyperbranched copolymer for water treatment applications.

Aquatic toxicity and mode of action of CdS and ZnS nanoparticles in four microalgae species

This study reports the differences in toxic action between cadmium sulfide (CdS) and zinc sulfide (ZnS) nanoparticles (NPs) prepared by recently developed xanthate-mediated method. The aquatic toxicity of the synthesized NPs on four marine microalgae species was explored. Growth rate, esterase activity, membrane potential, and morphological changes of microalgae cells were evaluated using flow cytometry and optical microscopy.CdS and ZnS NPs demonstrated similar level of general toxicity and growth-rate inhibition to all used microalgae species, except the red algae P. purpureum. More specifically, CdS NPs caused higher inhibition of growth rate for C. muelleri and P. purpureum, while ZnS NPs were more toxic for A. ussuriensis and H. akashiwo species. Our findings suggest that the sensitivity of different microalgae species to CdS and ZnS NPs depends on the chemical composition of NPs and their ability to interact with the components of microalgal cell-wall. The red microalga was highly resistant to ZnS NPs most likely due to the presence of phycoerythrin proteins in the outer membrane bound Zn2+ cations defending their cells from further toxic influence. The treatment with CdS NPs caused morphological changes and biochemical disorder in all tested microalgae species. The toxicity of CdS NPs is based on their higher photoactivity under visible light irradiation and lower dissociation in water, which allows them to generate more reactive oxygen species and create a higher risk of oxidative stress to aquatic organisms.The results of this study contribute to our understanding of the parameters affecting the aquatic toxicity of semiconductor NPs and provide a basis for further investigations.

Clarifying the roles of hydrothermal treatment and silica addition to synthesize TiO2-based nanocomposites with high photocatalytic performance

In this work we investigated the effect of hydrothermal treatment and silica addition on the structure and photocatalytic performance of synthesized TiO2-based nanocomposites. These materials were prepared by combining sol–gel process and hydrothermal treatment, and no templates or surfactants were used in these syntheses. The optimal synthesis conditions were investigated based on the variation of the preparation parameters. Anatase TiO2 crystals were synthesized without the need of a hydrothermal treatment, but this process appeared necessary to form an anatase phase with better structural quality and high photoactivity. The heat treatment step induced competitive phenomena toward the TiO2 structural properties and its photodegradation activity, but it proved to be advantageous as long as the pore structure, anatase phase, and high specific surface area were maintained. The addition of silica was then justified, aiming to stabilize the crystalline structure of TiO2 upon heat treatment. The ideal molar ratio of Si/(Si + Ti) was 0.2 for samples heat-treated at either 500 or 700 °C. The high photocatalytic efficiency of the synthesized nanocomposites is due to the combined effect of the photoactivity of TiO2 and adsorption capacity of SiO2. When compared with a commercial TiO2 sample (Degussa Evonik P25), increasing the catalyst loading proved to greatly enhance the performance of the synthesized nanocomposite, whereas the commercial one did not follow the same trend.

Synthesis of SnO2/yolk-shell LaFeO3 nanocomposites as efficient visible-light photocatalysts for 2,4-dichlorophenol degradation

Herein, yolk-shell LaFeO3 (YS-LFO) microsphere has been successfully prepared by a carbon microsphere (CMS) template-adsorption-calcination method. It was confirmed that the YS-LFO microspheres showed high visible-light photoactivities for 2,4-dichlorophenol degradation as compared to bare LaFeO3 (LFO) nanoparticles, attributing to the unique yolk-shell structure and the increased surface area. The visible-light photocatalytic activities of YS-LFO microspheres could be further promoted by coupling with SnO2 (SO) nanoparticles. Based on the surface photovoltage spectra, photoelectrochemical measurements and other characterization, it was demonstrated that the coupled SO afforded a thermodynamically suitable platform for accepting the high-level energy electrons from LaFeO3 so as to enhance the charge separation. Compared with YS-LFO microspheres and LFO nanoparticles, the amount optimized (10SO/YS-LFO) nanocomposites displayed 1.6 and 4.7-time enhancement for 2,4-dichlorophenol degradation under visible-light irradiation, respectively. This efficient strategy of morphology controlling and photoelectron modulating could pave the approach to design high-activity visible-light driven photocatalysts.

Effect of Graphene-Gold Nanocomposites on the Photocatalytic Activity Of TiO\(_2\)

The synthesis of graphene (Gr) - gold (Au) nanoparticle (NP) composite was achieved using continuous ultraviolet wave exposure. The functional groups were investigated with FT-IR spectra. From the Raman spectra, D-band and G-band of graphene were identified. As a result, the uniform deposition of nanometer-sized Au NPs on the graphene sheets was observed from the field emission scanning electron microscope (FE-SEM) images. The photodegradation of methylene blue in aqueous solutions is studied using various photocatalysts, including neat TiO2, Gr/TiO2 and Gr-Au/TiO2 composites. The Gr weight ratio in this research is 2%. The Gr2%-Au0.1%/TiO2 composite had the highest photoactivity.

Controlled synthesis of novel Z-scheme iron phthalocyanine/porous WO3 nanocomposites as efficient photocatalysts for CO2 reduction

Herein, novel Z-scheme iron phthalocyanine (FePc)/porous WO3 nanocomposites as efficient photocatalysts have been controllably synthesized based on the resulting porous WO3 pre-prepared by a hydrothermal process. The key is to make FePc assemble uniformly onto porous WO3 by hydroxyl induction for their close contacts via H-bonding. The optimized 0.8FePc/P-WO3 nanocomposite exhibits about 8-fold high photoactivity for reducing CO2 to CO and CH4 compared with the reported WO3 nanoplate, attributed to the increased specific surface, enhanced charge separation and extended visible-light utilization. Interestingly, the enhanced charge separation mainly depends on the novel Z-scheme transfer process with the un-overlapped optical absorption, along with the provided catalytic function of central Fe2+ in FePc for CO2 reduction mainly by means of the dual wavelength photocurrent action spectra, the electrochemical reduction tests, and the in-situ diffuse reflectance FTIR spectra. Moreover, it is also feasible to replace FePc with other MPcs.

Photocatalysis of rhodamine B and methyl orange degradation under solar light on ZnO and Cu2O thin films

We report the photocatalytic properties of ZnO and Cu2O thin films deposited on glass substrates at room temperature by DC sputtering and pulsed laser deposition. The photoactivity of the films was investigated through the degradation of rhodamine B (RhB) and methyl orange (MO) under solar light. In order to select the most suitable film of ZnO for the of RhB and MO degradation, the relationship between the characteristics (e.g. energy levels and defects concentration) of ZnO films and their effectiveness in the photocatalytic yield of RhB and MO been studied, where several films were deposited by using different oxygen partial pressures (PO2: 0.05–1.3 mbar), while Cu2O films were grown under a pressure of 0.01 mbar. The XRD patterns show that all ZnO films have (002) preferential orientation, and crystallite size increases from 73 to 122 nm raising PO2. The gap Eg of ZnO (3.26 and 4.15 eV) depends on PO2, and the films present photoluminescence emission in the UV–Vis-near IR region. On the basis of structural, optical and electrical characterizations of both films, a comparative study was carried out on the dyes degradation. Cu2O films exhibit a high photoactivity with MO (81.69%) under solar light (6 h), whilst for RhB the best elimination rate (60.85%) was achieved with ZnO films deposited at 0.1 mbar, which were also the ones exhibiting the highest PL peak intensity at the characteristic absorption wavelength of RhB (553 nm).

Oriented facet heterojunctions on CdS nanowires with high photoactivity and photostability for water splitting

The construction of a heterojunction structure with close contact and good light absorption capability is crucial to achieve the good photocatalytic H2 evolution performance. The heterostructure of photocatalyst with different orientations has proved to be an efficient strategy for photocatalytic water splitting. Herein, an oriented facet heterojunction (OFH) photocatalyst is reasonably designed with ZnIn2S4 nanosheets (ZIS NSs) and CdS nanowire (NW), in which strained interface between the two materials leads to high separation efficiency of electron-cavity. This heterostructure achieves photocatalytic H2 activity of 3072 μmol h−1 g−1 with excellent long-term stability (>30 h) under simulated solar light. By considering the interactions between atoms and electrons in the interface region, our density functional theory (DFT) calculation reveals the strong interfacial coupling between the ZnIn2S4 tip and the CdS stem. These findings open up a new platform of OFH-engineered nano-catalysts for more powerful and more efficient solar energy utilization and environmental applications.

Electrodeposited chromium-doped α-Fe2O3 under various applied potential configurations for solar water splitting

In this work, high quality hematite (α-Fe2O3) Chromium (Cr)-doped thin films have been synthesized via electrodeposition technique, on fluorine-doped tin oxide-coated glass substrates, under various applied potential configurations [cyclic voltammetry (CV), linear sweep voltammetry (LSV) and −0.5 V]. Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within 8%. The as-deposited films were subsequently annealed in air at 650 °C for 2 h. Our novel study highlights the effect of using variable potential approaches during the film preparation on the properties of Cr-αFe2O3 deposited films. The prepared thin films were analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV–Vis absorption and photoelectrochemical (PEC) analysis. XRD revealed that samples are crystallized in Cr-Fe2O3 cubic structure with a crystalline orientation in the plane (1 1 1) and a clear improvement of the crystallinity and size crystallite of the Cr-Fe2O3 deposited using CV process. SEM micrographs showed that the morphology grains were three-sided pyramid-shaped, expanding with increase of the crystallinity. The calculated band gap values are 2.18, 2.23 and 2.20 eV, respectively for −0.5 V, LSV, CV. The Cr-Fe2O3 films synthesized in this study showed high PEC activity with very low carrier density in comparison with the conventionally electrodeposited films. This Cr-doped hematite films ‘excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the α-Fe2O3 films.

Facet-charge-induced coupling dependent interfacial photocharge separation: A case of BiOI/g-C3N4 p-n junction

Heterojunction photocatalyst fabrication benefits the improvement of photocatalytic activity. However, the influence of different coupling facets receives less attention. Herein, two p-n junctions with different coupling facets of BiOI, denoted as B001/CN002 and B110/CN002+, were constructed by a simple precipitation method. In B001/CN002, BiOI nanosheets parallel combined with g-C3N4 with the {001} facet of BiOI and (002) plane of g-C3N4. After being treated by CTAB, the (002) plane of g-C3N4 shows positive charge (g-C3N4+), and the BiOI nanosheets were vertically assembled onto g-C3N4+. The results of photodegradation on multiform industrial contaminants and antibiotic revealed that B001/CN002 shows much higher photoactivity than g-C3N4, g-C3N4+, BiOI and B110/CN002+. The substantially facilitated charge separation and transfer at the interface of B001/CN002 promote the generation of 1O2 and O2−, accounting for the excellent photocatalytic activity. The study may provide a new perspective on designing heterostructured photocatalytic materials via facet-charge-induced interfacial engineering strategy.

Dependence of photoactivity of niobium pentoxide (Nb2O5) on crystalline phase and electrokinetic potential of the hydrocolloid

Multiphasic crystallite complex of the most popular photocatalyst – TiO2 has consistently shown better UV and/or visible photoactivity than its pristine monophasic counterparts. An identical behaviour is reported in the studies conducted on ZnO as well. This motivated the present study i) to explore the possibility to establish this as generic behavior for all such materials, and ii) to look for a better material with high photocatalytic activity. The choice of niobium pentoxide for the purpose lies in its uniqueness in terms of its existence in different oxidation states and crystalline phases. Additionally it offers a novel and promising alternative to the existing photoactive nanomaterials due to its apposite band gap, band edge location, stability, sorption characteristics and recyclability. Herein, an attempt has been made to prepare niobium pentoxide with different crystalline phases, including mixed, and analyze their photoactivity in UV and visible ranges. The results show that niobium pentoxide, calcined between 500-800°C, crystallizes predominantly in orthorhombic and 900°C and above in monoclinic phase. The results reveal that under both UV and visible radiation the monophasic (monoclinic phase) niobia has high photoactivity as compared to the other phases in degradation of aqueous probe pollutant. This result is contrary to the expected result. The samples have been characterized by X-ray diffraction(XRD), UV-VIS spectroscopy (UV-VIS DRS), X-ray photoelectron spectroscopy(XPS), photoluminescence(PL) spectroscopy, transmission electron microscopy(TEM), and scanning electron microscopy(SEM) to arrive at a conclusive explanation of the results. The sorption characteristics of the hydrocolloid system, among others, have been found to be responsible for this behavior.

Niobium Oxide Catalysts as Emerging Material for Textile Wastewater Reuse: Photocatalytic Decolorization of Azo Dyes

Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the developing areas of Northeast Brazil, which receives over 22 MJ m2 of natural sunlight irradiation annually. The application of photocatalytic treatment could incentivize water reuse practices in small and mid-sized textile businesses in the region. This work reports the facile synthesis of Nb2O5 catalysts and explores their performance for the treatment of colored azo dye effluents. The high photoactivity of this alternative photocatalyst makes it possible to quickly obtain complete decolorization, in less than 40 min of treatment. The optimal operational conditions are defined as 1.0 g L−1 Nb2O5 loading in slurry, 0.2 M of H2O2, pH 5.0 to treat up to 15 mg L−1 of methyl orange solution. To evaluate reutilization without photocatalytic activity loss, the Nb2O5 was recovered after the experience and reused, showing the same decolorization rate after several cycles. Therefore, Nb2O5 appears to be a promising photocatalytic material with potential applicability in wastewater treatment due to its innocuous character and high stability.

Evaluation of the Photocatalytic Activity of a Cordierite-Honeycomb-Supported TiO2 Film with a Liquid-Solid Photoreactor.

Anatase nanoparticles in suspension have demonstrated high photoactivity that can be exploited for pollutant removal in water phases. The main drawback of this system is the difficulty of recovering (and eventually reusing) the nanoparticles after their use, and the possible interference of inorganic salts (e.g., sulfates) that can reduce the performance of the photocatalyst. The present work describes the development of a cordierite-honeycomb-supported TiO2 film to eliminate the problems of catalyst recovery. The catalyst was then tested against phenol in the presence of increasing concentrations of sulfates in a specially developed recirculating modular photoreactor, able to accommodate the supported catalyst and scalable for application at industrial level. The effect of SO42− was evaluated at different concentrations, showing a slight deactivation only at very high sulfate concentration (≥3 g L−1). Lastly, in the framework of the EU project Project Ô, the catalyst was tested in the treatment of real wastewater from a textile company containing a relevant concentration of sulfates, highlighting the stability of the photocatalyst.

Electrophoretic deposition of flower-like CaBiVMoO8 particles for the photocatalytic degradation of pharmaceutical pollutants

In this work, it is reported for the first time the preparation of CaBiVMoO8 coatings by the electrophoretic deposition route. The material exhibits absorption in the visible light region with a bandgap energy of 2.49 eV. In addition, the conduction and valence potentials were estimated at 0.07 and 2.56 eV, respectively. Isopropanol-based suspensions of CaBiVMoO8 were used for the formation of the EPD coatings at 10, 12 and 14 V. The photocatalytic performance of the as-prepared coatings was examined by the degradation of the tetracycline antibiotic under UV–vis irradiation. The highest photoactivity was attained by the sample prepared at 12 V, which could be explained due to the more uniform deposition along the support under this applied voltage, increasing the formation of the photogenerated charge carriers though a better penetration and harvesting of the incident photons.

Electrodeposited Cr-Doped α-Fe2O3 thin films active for photoelectrochemical water splitting

Polycrystalline hematite (α-Fe2O3) Chromium (Cr)-doped thin films were electrodeposited on fluorine-doped tin oxide-coated glass substrates. The electrodeposition bath comprised an aqueous solution containing FeCl3·6H2O, NaCl, and H2O2.Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within the 2–8 at. % range. The as-deposited films were subsequently annealed in air at 650 °C for 2 h. The structure and morphological characteristics of the undoped and Cr-doped α-Fe2O3 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectroscopy. Cr doping led the main XRD lines to shift to lower angles, which mostly resulted from substituting Fe3+ for Cr4+ ions that leads to α-Fe2O3 lattice contraction. The SEM observations showed that the roughness and aspect of surfaces changed with the Cr doping level. The photoelectrochemical (PEC) performance of the α-Fe2O3 films was examined by chronoamperometry and linear sweep voltammetry techniques. The Cr-doped films exhibited greater photoelectrochemical activity than the undoped α-Fe2O3 thin films. The highest photocurrent density was obtained for the 8% Cr-doped α-Fe2O3 films in 1 M NaOH electrolyte. All the samples achieved their best IPCE at 400 nm. The IPCE values for the 8 at.% Cr-doped hematite films were 20-fold higher than that of the undoped sample.This Cr-doped hematite films ‘excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the α-Fe2O3 films.

Novel Z-scheme Co3O4/WO3 nanocomposite performance in adsorption and photocatalytic degradation of ethylparaben and methylene blue in water

Effective removal of organic pollutants from water bodies using both adsorption and photocatalysis provides an effective solution for both ecological and environmental importance. Degradation of organics such as parabens using photocatalytic process with visible light irradiation is challenging. However, semiconductor photocatalysis based on solar radiation utilisation whose mechanism involves absorption of photons when irradiated by sunlight or illuminated light, is possible. WO3 has been exploited for its visible light utilisation whereas a novel Z–scheme photocatalyst formed when WO3 is doped with Co3O4 has shown enhanced photocatalysis and adsorption performance. Z-scheme WO3/Co3O4 semiconductor nanocomposite exhibits high photoactivity due to the suitable band gap matching between the two semiconductors as they share photoexcited electrons in the conduction band (CB) that can easily migrate to each other’s valence band (VB) to recombine with holes under solar light irradiation. In the present work, novel Co3O4/WO3 (ratio 3:7) nanocomposites were successfully synthesised via two-step route including the solvothermal process and subsequent wet impregnation method. The Co3O4/WO3 nanocomposites were applied for efficient removal of methylene blue and ethylparaben from water. Powder x-ray diffractometer (pXRD), scanning electron microscope (SEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), x–ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) were used to characterise the prepared nanocomposites. The adsorption and photocatalytic activities of WO3 and Z-scheme Co3O4/WO3 nanocomposites (30 wt% of Co3O4) were evaluated by monitoring adsorption and photocatalytic activities of methylene blue and ethylparaben from water. The results confirmed that adsorption and photoactivity efficiencies of Co3O4/WO3 nanocomposites were higher than either WO3 or Co3O4 individually. The percentage removal efficiencies using Z-scheme Co3O4/WO3 in the degradation of methylene blue and ethylparaben were 100% and 88% respectively, after 15 min. The improvement of adsorption capability could be attributed to the increase of specific surface areas by addition of Co3O4 whereas photocatalytic performance may be attributed to lower recombination rates. Furthermore, the effects of water parameters and radical scavengers on the adsorption and degradation processes were also investigated. It was noted that were major active species in the removal of methylene blue and ethylparaben. A probable mechanism on the enhanced photocatalytic performance was proposed based on the band structure and radical trapping experiment. The novel Z-scheme Co3O4/WO3 nanocomposite developed in this study has great potential for degradation of organic pollutants in wastewater matrix. To the best of our knowledge, there is no literature that has reported the synthesis of Co3O4/WO3 nanocomposite for the application of removal of organic pollutants.

A Highly Efficient Composite Catalyst Constructed From NH2-MIL-125(Ti) and Reduced Graphene Oxide for CO2 Photoreduction.

Substantial consumption of fossil fuels causes an increase in CO2 emissions and intensifies global pollution problems, such as the greenhouse effect. Recently, a new type of ultra-low-density porous material, metal-organic frameworks (MOFs), has been developed for the photocatalytic conversion of CO2. Herein, a composite photocatalytic catalyst based on NH2-MIL-125(Ti) and reduced graphene oxide (rGO@NH2-MIL-125) was fabricated through a facile “one-pot” process. The acquired materials were characterized to obtain their structures, morphologies, and optical information. The experimental results showed that methyl formate (MF) was the predominant reaction product, and rGO@NH2-MIL-125 exhibited the highest yield of 1,116 μmol·g−1·h−1, more than twice that of pure MIL-125. The high photoactivity of rGO@NH2-MIL-125 can be ascribed to the effective spatial separation and transfer of photoinduced carriers, largely due to the synergistic effect of amino functionality and rGO incorporation. rGO@NH2-MIL-125 also displayed acceptable repeatability in cyclic runs for CO2 reduction.

Improved Photoactivities of Large‐surface‐area g‐C3N4 for CO2 Conversion by Controllably Introducing Co‐ and Ni‐Species to Effectively Modulate Photogenerated Charges

AbstractSimultaneously modulating photogenerated electrons and holes by introducing transitional metals species on carbon nitride (g‐C3N4) are highly desired for effectively photocatalytic converting CO2. Herein, a cyanuric acid‐melamine preassembled approach is developed to obtain large‐surface‐area g‐C3N4 with high photoactivity for CO2 conversion, and its photoactivity is improved by controllably modifying Co‐species during the synthetic process of g‐C3N4, attributed to its hole capture capability and catalytic capability for water oxidation. Moreover, the photoactivity is further improved by decorating Ni‐species on g‐C3N4, attributed to its electron capture capability and catalytic capability for CO2 reduction. Noticeably, simultaneously modulating holes and electrons displays a noticeable synergy on improving photocatalytic activities. Interestingly, the photoactivity of amount‐optimized Co and Ni co‐modified g‐C3N4 is 3.1‐time higher than that of pristine g‐C3N4, with the quantum efficiency improvement of 4.5 time at 405 nm. This work will provide a feasible way of simultaneously modulating electrons and holes to fabricate high‐performance g‐C3N4‐based nano‐sized photocatalysts for CO2 conversion.

Effect of the carbon loading on the structural and photocatalytic properties of reduced graphene oxide-TiO2 nanocomposites prepared by hydrothermal synthesis

This work deals with the preparation of reduced graphene oxide (RGO)-TiO2 composites by a one-step hydrothermal treatment. The effect of the RGO loading on both the structural properties and photocatalytic behavior of RGO-TiO2 is deeply addressed herein. The hydrothermal treatment promoted the reduction of graphene oxide, crystallization of TiO2 into anatase, and anchoring of TiO2 nanoparticles on RGO sheets. It was observed that the prepared anatase particles showed sizes below 10nm, whereas the RGO sheets displayed thicknesses smaller than 1nm. The use of RGO at concentrations up to 15wt% greatly increased the specific surface area of RGO-TiO2. It was demonstrated that the combination of RGO and TiO2 gives rise to materials with improved photocatalytic properties and tailored structural properties. The composite with the highest photoactivity was the one containing an RGO loading of 1wt%; this composite displayed a photocatalytic rate constant about 9.5 times higher than that evaluated for pure TiO2. This behavior may be related to the stacking of RGO nanosheets when its concentration is above 1wt%. Moreover, the addition of RGO in excess may prevent the activation of the TiO2 surface by UV light and also decrease the lifetime of the photogenerated electron-hole pairs. Therefore, it appears that 1wt% is the optimal loading of RGO to obtain a close interfacial contact between RGO and TiO2, leading to both an effective activation of TiO2 by UV radiation and an enhanced charge transfer between RGO and TiO2.

A promising inorganic-organic Z-scheme photocatalyst Ag3PO4/PDI supermolecule with enhanced photoactivity and photostability for environmental remediation

Silver orthophosphate (Ag3PO4) based semiconductor photocatalysis have been widely investigated for environmental purification due to its strong oxidation ability. Yet, its poor photostability and low photoactivity hamper its extensive applications. Here, an inorganic-organic Z-scheme photocatalytic system for antibiotic degradation demonstrated high photoactivity and stability through the use of Ag3PO4/Perylene diimide organic supermolecule (PDIsm). The apparent rate constant of tetracycline hydrochloride (TC-H) degradation with Ag3PO4/PDIsm was 1.5 times that of Ag3PO4 and 8 times that of PDIsm. The photocatalytic activity of Ag3PO4/PDIsm toward TC-H still kept 65 % after four reuses, while pure Ag3PO4 only kept 22 %. We revealed that this high photoactivity and photostability arisen from the efficient carriers separation and the formation of direct Z-scheme junction. Importantly, this Z-scheme electron transfer pathway was confirmed by thorough experimental study and density functional theory (DFT) calculation. This work demonstrated the significant potential of Ag3PO4-based inorganic-organic Z-scheme photocatalyst in environmental remediation.