Tuning near-gap electronic structure, interface charge transfer and visible light response of hybrid doped graphene and Ag3PO4 composite: Dopant effects.
ABSTRACT: The enhanced photocatalytic performance of doped graphene (GR)/semiconductor nanocomposites have recently been widely observed, but an understanding of the underlying mechanisms behind it is still out of reach. As a model system to study the dopant effects, we investigate the electronic structures and optical properties of doped GR/Ag3PO4 nanocomposites using the first-principles calculations, demonstrating that the band gap, near-gap electronic structure and interface charge transfer of the doped GR/Ag3PO4(100) composite can be tuned by the dopants. Interestingly, the doping atom and C atoms bonded to dopant become active sites for photocatalysis because they are positively or negatively charged due to the charge redistribution caused by interaction. The dopants can enhance the visible light absorption and photoinduced electron transfer. We propose that the N atom may be one of the most appropriate dopants for the GR/Ag3PO4 photocatalyst. This work can rationalize the available experimental results about N-doped GR-semiconductor composites, and enriches our understanding on the dopant effects in the doped GR-based composites for developing high-performance photocatalysts.
Project description:Composites comprised of Ag3PO4 and bare TiO2 (TiO2@Ag3PO4) or silver doped TiO2 (Ag@TiO2-Ag3PO4) have been synthesized by coupling sol-gel and precipitation methods. For the sake of comparison, also the bare components have been similarly prepared. All the samples have been characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), photoelectrochemical measurements, and specific surface area (SSA) analysis. The optoelectronic and structural features of the samples have been related to their photocatalytic activity for the degradation of 4-nitrophenol under solar and UV light irradiation. Coupling Ag3PO4 with silver doped TiO2 mitigates photocorrosion of the Ag3PO4 counterpart, and remarkably improves the photocatalytic activity under solar light irradiation with respect to the components, to the TiO2-Ag3PO4 sample, and to the benchmark TiO2 Evonik P25. These features open the route to future applications of this material in the field of environmental remediation.
Project description:Bacterial and organic pollutants are major problems with potential adverse impacts on human health and the environment. A promising strategy to alleviate these impacts consists in designing innovative photocatalysts with a wider spectrum of application. In this paper, we report the improved photocatalytic and antibacterial activities of chemically precipitated Ag3PO4 microcrystals by the incorporation of W at doping levels 0.5, 1, and 2 mol %. The presence of W directly influences the crystallization of Ag3PO4, affecting the morphology, particle size, and surface area of the microcrystals. Also, the characterization via experimental and theoretical approaches evidenced a high density of disordered [AgO4], [PO4], and [WO4] structural clusters due to the substitution of P5+ by W6+ into the Ag3PO4 lattice. This leads to new defect-related energy states, which decreases the band gap energy of the materials (from 2.27 to 2.04 eV) and delays the recombination of e'-h• pairs, leading to an enhanced degradation process. As a result of such behaviors, W-doped Ag3PO4 (Ag3PO4:W) is a better visible-light photocatalyst than Ag3PO4, demonstrated here by the photodegradation of potential environmental pollutants. The degradation of rhodamine B dye was 100% in 4 min for Ag3PO4:W 1%, and for Ag3PO4, the obtained result was 90% of degradation in 15 min of reaction. Ag3PO4:W 1% allowed the total degradation of cephalexin antibiotic in only 4 min, whereas pure Ag3PO4 took 20 min to achieve the same result. For the degradation of imidacloprid insecticide, Ag3PO4:W 1% allowed 90% of degradation, whereas Ag3PO4 allowed 40%, both in 20 min of reaction. Moreover, the presence of W-dopant results in a 16-fold improvement of bactericidal performance against methicillin-resistant Staphylococcus aureus. The outstanding results using the Ag3PO4:W material demonstrated its potential multifunctionality for the control of organic pollutants and bacteria in environmental applications.
Project description:Black NiO powders were prepared by a hydrothermal method. Moreover, the visible light-driven Ag3PO4/NiO photocatalyst composites were successfully synthesized by in situ precipitation method. These samples were structurally characterized by X-ray diffraction and Rietveld refinement. The strong interaction between the phases and the defects in the samples was affected by the formation of the composites, as identified by Fourier transform infrared spectroscopy and Raman spectroscopy. UV-vis diffuse reflectance spectroscopy exhibited enhanced light absorption for all Ag3PO4/NiO composites, suggesting the effective interaction between the phases. Moreover, field-emission scanning electron microscopy images revealed the presence of NiO microflowers composed of nanoflakes in contact with Ag3PO4 microparticles. The composite with 5% NiO presented enhanced photocatalytic efficiency in comparison with pure Ag3PO4, degrading 96% of rhodamine B (RhB) dye in just 15 min under visible light; however, the recycling experiments confirmed that the composite with 75% NiO showed superior stability. The recombination of the electron-hole pairs was considered for the measurement of the photoluminescence of the samples. These measurements were performed to evaluate the possible causes for the difference in the photocatalytic responses of the composites. From these experimental results, possible photocatalytic mechanisms for RhB degradation over Ag3PO4/NiO composites under visible-light irradiation were proposed.
Project description:In this study, a novel graphene/Ag3PO4 quantum dot (rGO/Ag3PO4 QD) composite was successfully synthesized via a facile one-step photo-ultrasonic-assisted reduction method for the first time. The composites were analyzed by various techniques. According to the obtained results, Ag3PO4 QDs with a size of 1-4 nm were uniformly dispersed on rGO nanosheets to form rGO/Ag3PO4 QD composites. The photocatalytic activity of rGO/Ag3PO4 QD composites was evaluated by the decomposition of methylene blue (MB). Meanwhile, effects of the surfactant dosage and the amount of rGO on the photocatalytic activity were also investigated. It was found that rGO/Ag3PO4 QDs (WrGO:Wcomposite = 2.3%) composite exhibited better photocatalytic activity and stability with degrading 97.5% of MB within 5 min. The improved photocatalytic activities and stabilities were majorly related to the synergistic effect between Ag3PO4 QDs and rGO with high specific surface area, which gave rise to efficient interfacial transfer of photogenerated electrons and holes on both materials. Moreover, possible formation and photocatalytic mechanisms of rGO/Ag3PO4 QDs were proposed. The obtained rGO/Ag3PO4 QDs photocatalysts would have great potentials in sewage treatment and water splitting.
Project description:In this work, a series of heterostructure Ag@Ag3PO4/g-C3N4/NiFe layered double hydroxide (LDH) nanocomposites were prepared by a combination of an electrostatic self-assembly and in situ photoreduction method. In this method, positively charged p-type Ag3PO4 was electrostatically bonded to the self-assembled negatively charged surface of the n-n-type g-C3N4/NiFe (CNLDH) LDH hybrid material with partial reduction of Ag+ to metallic Ag nanoparticles (NPs) by the photogenerated electrons and available surface -OH groups of LDH under visible light irradiation. The presence of Ag3PO4 as a p-type semiconductor, the surface plasmon resonance (SPR) effect of metallic Ag NPs, and oxygen vacancies as Ov-type defects in NiFe LDH could greatly achieve the quasi-type-II p-n/n-n dual heterojunctions, which was revealed by the shifted conduction band and valence band potentials in Mott-Schottky (M-S) analysis. Among all the optimized heterostructures, CNLDHAgP4 could achieve the highest photocatalytic Cr(VI) reduction rate of 97% and phenol oxidation rate of 90% in 2 h. The heterostructure CNLDHAgP4 photocatalyst possesses a unique morphology consisting of cubic phases of both Ag NPs and Ag3PO4, which adhered to the thin and curvy layers of the CNLDH hybrid for smooth electronic and ionic charge transport. Furthermore, the intimate Schottky barriers formed at the interface of quasi-type-II p-n/n-n dual heterojunctions were verified by the photoluminescence, linear sweep voltammetry, M-S, electrochemical impedance study, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy studies. The SPR effect of Ag NPs and oxygen vacancies as Ov-type defect in NiFe LDH can effectively accelerate the threshold of charge separation and be the main reason for the enhanced activity achieved by the as-fabricated heterostructure photocatalyst.
Project description:These data inform about the XPS profile of Ag4d, P2p, and O1s from the samples of Ag3PO4, defect-Ag3PO4, Ag3PO4/PtCl6 2- and defect-Ag3PO4/PtCl6 2- which were denoted as AP, DAP, AP/Pt, and DAP/Pt, respectively. These samples were made by co-precipitation method using the starting material of silver nitrate (AgNO3), disodium hydrogen phosphate dodecahydrate (Na2HPO4.12H2O), and hexachloroplatinic acid hexahydrate (H2PtCl6.6H2O) for platinum complexes dopant. The water solution and mixed water-ethanol solution for dissolving the AgNO3 were used for free-defect and defect samples, respectively. The Ag4d, P2p, and O1s of these samples were investigated using the XPS. The deconvolutions of O1s peak were analyzed using the software of XPSPEAK Version 4.1. The modification of Ag3PO4 by defect and platinum complexes dopant had changed the curve profile of Ag4d, P2p and O1s. Two types of oxygen of O-1 and O-2 were observed in O1s spectrum. The ratios of O-2/O-1 with the value of 0.25, 0.32, 0.49 and 0.51 were found in the sample of AP, DAP, AP/Pt, and DAP/Pt, respectively. These data are related to the research article "The surface modification of Ag3PO4 using anionic platinum complexes for enhanced visible-light photocatalytic activity" .
Project description:Phosphate ( PO43- ) modification of semiconductor photocatalysts such as TiO2, C3N4, BiVO4, and etc. has been shown positive effect on the enhancement of photocatalytic performance. In the present study, we demonstrate a novel one-pot surface modification route on Ag3PO4 photocatalyst by ammonium phosphate [(NH4)3PO4], which combines PO43- modification with ammonium ( NH4+ ) etching to show multiple effects on the structural variation of Ag3PO4 samples. The modified Ag3PO4 photocatalysts exhibit much higher photocatalytic performance than bare Ag3PO4 for the degradation of organic dye solutions under visible light irradiation. It is indicated that the NH4+ etching favors the surface transition from Ag3PO4 to metallic Ag nanoparticles, resulting in the fast capture of photogenerated electrons and the followed generation of O2·- radicals. The strongly adsorbed PO43- on the Ag3PO4 surfaces can further provide more negative electrostatic field, which improves the separation of photogenerated electron-hole pairs by inducing the holes to directly flow to the surface and then enhances the formation of reactive ·OH radicals. Furthermore, the photocatalytic performance of the modified Ag3PO4 photocatalysts can be optimized by monitoring the concentration of (NH4)3PO4 that is 1 mM.
Project description:The transition energies and formation energies of N, C, F, Cl, and S as substitutional dopants in Ag3PO4 are studied using first-principles calculations based on the hybrid Hartree-Fock density functional, which correctly reproduces the band gap and thus provides the accurate defect states. Our results show that NO and CO act as deep acceptors, FO, ClO, and SP act as shallow donors. NO and CO have high formation energies under O-poor condition therefore they are not suitable for p-type doping Ag3PO4. Though FO, ClO, and SP have shallow transition energies, they have high formation energies, thus FO, ClO, and SP may be compensated by the intrinsic defects (such as Ag vacancy) and they are not possible lead to n-type conductivity in Ag3PO4.
Project description:A new visible-light-responsive tetrahedral ultrathin metal-organic framework nanosheet (UMOFNs)/Ag3PO4 composite photocatalyst with a core-shell structure was readily synthesized by sonication in an organic solvent. Characterization methods for the photocatalyst included X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectroscopy. The XRD patterns of the composite photocatalyst before and after visible-light irradiation demonstrated that trace amounts of Ag ions in the composite photocatalyst easily transformed into Ag nanoparticles, which play a role in promoting charge separation at the interface of a heterojunction. The UMOFNs/Ag3PO4 composite photocatalyst showed higher photocatalytic activity for the photodegradation of 2-chlorophenol (2-CP) under visible-light irradiation (>420 nm) than Ag3PO4. The complete degradation of 2-CP was achieved in 7 min using the tetrahedral UMOFNs/Ag3PO4 core-shell photocatalyst, and the apparent reaction rate was approximately 26 times higher than that of pure Ag3PO4. Further, a scavenger experiment showed h+ and O2 •- were the major reactive species involved in the photocatalytic reaction system. This enhanced photocatalytic activity results from the efficient separation of photoinduced electron-hole pairs and the increase of interface area between Ag3PO4, UMOFNs, and the Ag nanoparticles.
Project description:Chemical doping has been widely used to finely tune the electrical properties of organic hole-transporting materials (HTMs) that find widespread applications in perovskite solar cells (PSCs). Here, to shed light on the precise role of chemical p-doping in affecting the charge-transport properties of HTMs and photovoltaic performance of PSCs, two kinds of representative dopants, including lithium bis(trifluoromethane)sulfonimide (LiTFSI) and two Co(III) complexes tris[2-(1H-pyrazol-1-yl)-4-tert-butylpyridine]cobalt(III)tris[bis(trifluoromethylsulfonyl)imide] (FK209) and tris[2-(1H-pyrazol-1-yl)pyridine]cobalt(III)tris[bis(trifluoromethylsulfonyl)imide] (FK102), are employed as the p-type dopant models to dope the 2,2',7,7'-tetrakis[N,N-di-p-methoxyphenylamine]-9,9'-spirobifluorene (spiro-OMeTAD) HTM. Both dopants can facilitate the generation of oxidized spiro-OMeTAD radical cation and improve hole mobility. Co-doping of FK209 and LiTFSI is necessary to achieve an optimal doping property and best device performance with power conversion efficiency of 17.8% compared to that of the FK209-doped device (13.5%) and the LiTFSI-doped device (15%). UV-vis absorption, space-charge-limited current measurements, and steady-state and time-resolved photoluminescence measurements have confirmed that with the co-doping of the two kinds of p-dopants in a proper ratio the doped spiro-OMeTAD exhibits a high charge carrier mobility and charge carrier transfer/collection capability.