Ternary Pt@TiO2/rGO Nanocomposite to Boost Photocatalytic Activity for Environmental and Energy Use

This work explores the effect of ternary nanostructure for the enhanced photocatalytic degradation of pollutants and dyes. One-pot solvothermal-assisted approach was used for producing nanosized Pt@TiO₂ hybrid nanoparticles (NPs) decorated on reduced graphene oxide (rGO) layers. The microstructure, morphology, chemical composition, and optical absorption of the designed photocatalyst was successfully characterized (using XRD, TEM, Raman, UV–visible absorption spectra, and XPS techniques). The ternary Pt@TiO₂-rGO photocatalyst consist of monodisperse quasi-spherical Pt@TiO₂ NPs with an average size of 11 nm deposited on the rGO nanosheets. Furthermore, Pt@TiO₂-rGO was further investigated for the photodegradation of pesticide and dyes under UV and visible light. The ternary Pt@TiO₂-rGO photocatalyst proved a significant improvement on the photodecomposition of pollutants compared to hybrid Pt@TiO₂. The Pt@TiO₂-rGO photocatalyst was found to show seven- and threefold increase in the photocatalytic activity compared to TiO₂ and Pt@TiO₂ NPs, respectively which resulted from the high surface area of rGO and as well as the strong Pt/TiO₂/rGO interactions which ensured excellent properties of charge separation. On the other hand, the ternary photocatalyst exhibited very good recycle and reuse capacity up to five cycles.

     

Improved Photocatalytic Activity Using Ternary Au-ZnO/rGO Nanocomposite

In the present study, ternary Au-ZnO/rGO nanocomposite was prepared using a modified polyol protocol. The ternary structure was attained by deposition of both gold nanoparticles (AuNPs) and ZnO NPs on the rGO surface. No surfactants or ligands are used in this chemical process. On the other hand, 1,3-propanediol was used as solvent, reducing agent and surfactant to ensure the formation of NPs and inhibit particles accumulation. The XRD data confirm the successful formation of the three materials and the high crystallinity of the as-prepared sample. Moreover, the XPS measurements confirmed the high purity of the nanocomposite. TEM images show the formation of ternary Au/ZnO/rGO nanostructure. However, Au and ZnO NPs exhibited spherical shape with an average size of 20 nm and homogeneously distribution onto the rGO surface. The ternary Au-ZnO/rGO nanocomposite exhibited optical response in both UV and visible region due to the plasmonic properties of AuNPs. The BET data revealed an increase of the surface area of Au-ZnO/rGO nanocomposite compared to bare ZnO and hybrid Au-ZnO NPs which render it a promising system for high photocatalytic activity. The preliminary photodegradation measurements against MB molecules prove the high performance of the ternary Au-ZnO/rGO nanocomposite to decompose pollutant molecules compared to bare ZnO. The observed photocatalytic activity enhancement could be attributed to the apport given by both plasmonic properties of AuNPs and the high surface area of rGO.

     

Crystalline ZnO and ZnO/TiO2 nanoparticles derived from tert-butyl N-(2 mercaptoethyl)carbamatozinc(II) chelate: Electrocatalytic studies for H2 generation in alkaline electrolytes

A newly synthesized zinc(II) complex, namely tert-butyl N-(2 mercaptoethyl)carbamatozinc(II) complex [Zn(Boc-S)₂] (Boc = tert-butyl N-[2-mercaptoethyl]carbamate), has been used as an organozinc precursor for the production of crystalline ZnO and ZnO/TiO₂ nanoparticles. The synthesized complex and the obtained nanomaterials were fully characterized using various spectroscopic and surface analysis techniques. Their surface morphology, chemical purity and stoichiometry have been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) as well as X-ray fluorescence. The synthesized Zn(II) molecular complex, ZnO and ZnO/TiO₂ nanomaterials have been tested in alkaline aqueous solution (1.0 MNaOH) for the hydrogen evolution reaction (HER) using various electrochemical techniques. The results revealed high HER catalytic performance of ZnO and ZnO/TiO₂ cathode materials, with the latter exhibiting higher catalytic activity recording an exchange current density (j_o) of 0.3 mA cm⁻². This current value, which approaches that of Pt wire (0.5 mA cm⁻²), cross-sectional area ~0.008 cm², is about 11 and 100 times greater than those measured for ZnO alone (0.028 mA cm⁻²) and TiO₂ alone (0.0032 mA cm⁻²), respectively. Moderate catalytic activity was recorded for the complex catalyst, namely GC-Zn(Boc-S)₂ with j_o value of (0.01 mA cm⁻²). Tafel slope values of 130 and 122 mV dec⁻¹ were calculated for ZnO and ZnO/TiO₂, respectively. Such Tafel slope values, which are close to that of the Pt wire (120 mV dec⁻¹), referred to a Volmer-controlled HER kinetics. Other important electrochemical parameters describing the kinetics of the HER, such as roughness factor (R_f) and turnover frequency (TOF) were also estimated and discussed. The high numerical values of the various HER kinetic parameters recorded for the ZnO/TiO₂ catalyst, in addition to its high stability and durability (stable for up to 10 000 continuous cathodic polarization cycles), besides maintaining its morphology and chemical composition after stability test (confirmed from SEM/EDX and XRD examinations), located it in a privileged position among the most efficient HER electrocatalysts reported in the literature.