Fazal Raziq

Synthesis of silicate-bridged ZnO/g-C3N4 nanocomposites as efficient photocatalysts and its mechanism

In this study, silicate-capped ZnO/g-C3N4 nanocomposites were successfully fabricated by a simple wet chemical process. The photocatalytic activities of g-C3N4 for the degradation of phenol and the production of H2 are greatly enhanced after coupling with an appropriate amount of nanocrystalline ZnO. This is attributed to the prolonged lifetime and increased separation of the photogenerated charges, which are mainly based on atmosphere-controlled steady-state surface photovoltage spectra and time-resolved surface photovoltage responses. Interestingly, the lifetime and separation of photogenerated charges are further improved after the introduction of silicate groups as linkers between ZnO and g-C3N4, which consequently lead to enhanced photocatalytic activities, as much as 4 times higher compared to g-C3N4. Evidently, the built silicate linkers, which act as bridges, are highly favorable for charge transfer and separation in the fabricated heterojunctional nanocomposites and also for efficient photocatalysis. The present work provides a simple and feasible idea to enhance photogenerated charge separation so as to improve the photoactivities of nanocomposites.

Coupling of Nanocrystalline Anatase TiO2 to Porous Nanosized LaFeO3 for Efficient Visible-Light Photocatalytic Degradation of Pollutants

In this work we have successfully fabricated nanocrystalline anatase TiO2/perovskite-type porous nanosized LaFeO3 (T/P-LFO) nanocomposites using a simple wet chemical method. It is clearly demonstrated by means of atmosphere-controlled steady-state surface photovoltage spectroscopy (SPS) responses, photoluminescence spectra, and fluorescence spectra related to the formed OH− radical amount that the photogenerated charge carriers in the resultant T/P-LFO nanocomposites with a proper mole ratio percentage of TiO2 display much higher separation in comparison to the P-LFO alone. This is highly responsible for the improved visible-light activities of T/P-LFO nanocomposites for photocatalytic degradation of gas-phase acetaldehyde and liquid-phase phenol. This work will provide a feasible route to synthesize visible-light responsive nano-photocatalysts for efficient solar energy utilization.

Prolonged lifetime and enhanced separation of photogenerated charges of nanosized α-Fe2O3 by coupling SnO2 for efficient visible-light photocatalysis to convert CO2 and degrade acetaldehyde

To develop efficient visible-light photocatalysis on α-Fe2O3, it is highly desirable to promote visible-light-excited high-energy-level electron transfer to a proper energy platform thermodynamically. Herein, based on the transient-state surface photovoltage responses and the atmosphere-controlled steady-state surface photovoltage spectra, it is demonstrated that the lifetime and separation of photogenerated charges of nanosized α-Fe2O3 are increased after coupling a proper amount of nanocrystalline SnO2. This naturally leads to greatly improved photocatalytic activities for CO2 reduction and acetaldehyde degradation. It is suggested that the enhanced charge separation results from the electron transfer from α-Fe2O3 to SnO2, which acts as a proper energy platform. Based on the photocurrent action spectra, it is confirmed that the coupled SnO2 exhibits longer visible-light threshold wavelength (~590 nm) compared with the coupled TiO2 (~550 nm), indicating that the energy platform introduced by SnO2 would accept more photogenerated electrons from α-Fe2O3. Moreover, electrochemical reduction experiments proved that the coupled SnO2 possesses better catalytic ability for reducing CO2 and O2. These are well responsible for the much efficient photocatalysis on SnO2-coupled α-Fe2O3.

高光催化活性的磷氧桥连TiO 2 /g-C 3 N 4 纳米复合体的合成

Abstract One of the most general methods to enhance the separation of photogenerated carriers for g-C3N4 is to construct a suitable heterojunctional composite, according to the principle of matching energy levels. The interface contact in the fabricated nanocomposite greatly influences the charge transfer and separation so as to determine the final photocatalytic activities. However, the role of interface contact is often neglected, and is rarely reported to date. Hence, it is possible to further enhance the photocatalytic activity of g-C3N4-based nanocomposite by improving the interfacial connection. Herein, phosphate–oxygen (P–O) bridged TiO2/g-C3N4 nanocomposites were successfully synthesized using a simple wet chemical method, and the effects of the P–O functional bridges on the photogenerated charge separation and photocatalytic activity for pollutant degradation and CO2 reduction were investigated. The photocatalytic activity of g-C3N4 was greatly improved upon coupling with an appropriate amount of nanocrystalline TiO2, especially with P–O bridged TiO2. Atmosphere-controlled steady-state surface photovoltage spectroscopy and photoluminescence spectroscopy analyses revealed clearly the enhancement of photogenerated charge separation of g-C3N4 upon coupling with the P–O bridged TiO2, resulting from the built P–O bridges between TiO2 and g-C3N4 so as to promote effective transfer of excited electrons from g-C3N4 to TiO2. This enhancement was responsible for the improved photoactivity of the P–O bridged TiO2/g-C3N4 nanocomposite, which exhibited three-time photocatalytic activity enhancement for 2,4-dichlorophenol degradation and CO2 reduction compared with bare g-C3N4. Furthermore, radical-trapping experiments revealed that the OH species formed as hole-modulated direct intermediates dominated the photocatalytic degradation of 2,4-dichlorophenol. This work provides a feasible strategy for the design and synthesis of high-performance g-C3N4-based nanocomposite photocatalysts for pollutant degradation and CO2 reduction.

Role of quaternary N in N-doped graphene–Fe2O3 nanocomposites as efficient photocatalysts for CO2 reduction and acetaldehyde degradation

The quaternary N in N-doped graphene–Fe2O3 nanocomposites could be very favorable for the transfer and transportation of photogenerated charges and for the adsorption of CO2 and O2 so as to greatly enhance the charge separation, leading to the obviously-improved photoactivities for CO2 reduction to selectively evolve CO and for acetaldehyde degradation.

Enhanced photoelectrochemical activities for water oxidation and phenol degradation on WO 3 nanoplates by transferring electrons and trapping holes

It is highly desired to improve the photoelectrochemical (PEC) performance of nanosized WO3 by artificially modulating the photogenerated electrons and holes simultaneously. Herein, WO3 nanoplates have been successfully prepared by a simple one-pot two-phase separated hydrolysis-solvothermal method, and then co-modified with RGO and phosphate acid successively by wet chemical processes. Subsequently, the as-prepared WO3-based nanoplates were immobilized on the conductive glasses to explore the PEC activities for both water oxidation to evolve O2 and phenol degradation. It is clearly demonstrated that the co-modified WO3 nanoplates exhibit significantly improved PEC activities compared with pristine WO3, especially for that with the amount-optimized modifiers by ca. 6-time enhancement. Mainly based on the evaluated hydroxyl radical amounts produced and the electrochemical impedance spectra, it is suggested that the improved PEC activities are attributed to the greatly enhanced photogenerated charge separation after chemically modification with RGO and phosphate groups to WO3, respectively by transferring electrons as the collectors and trapping holes via the formed negative field after phosphate disassociation. This work provides a feasible synthetic strategy to improve the photoactivities of nanosized WO3 for energy production and environmental remediation.