Photocatalytic reduction for graphene oxide by PbTiO3 with high polarizability and its electrocatalytic application in pyrrole detection

Electronic and electrocatalytic properties of PbTiO3: unveiling the effect of strain and oxygen vacancy

First-principles calculations based on density-functional theory have been used to investigate the effect of biaxial strain and oxygen vacancy on the electronic, photocatalytic, and electrocatalytic properties of PbTiO3 oxide. Our results show that PbTiO3 has a high exciton binding energy and a band gap that can be easily moderated with different strain regimes. From a reactivity viewpoint, the highly exothermic adsorption of hydrogen atoms in both pristine and strained PbTiO3 structures does not make it a potential electrocatalyst for the hydrogen evolution reaction. Fortunately, the presence of oxygen vacancies on the PbTiO3 surface induces moderate adsorption energies, making the reduced PbTiO3 suitable for hydrogen evolution reaction processes.

Meso-tetra(4-sulfonatophenyl)porphyrin silver/Ag nanoparticles/graphene-phase C3N4 with a sandwich-like structure and double-faced active centers via two-step room-temperature photocatalytic synthesis for ractopamine detection

Photochemical synthesis under visible light irradiation is a novel approach in the field of green chemistry, and composites with abundant active centers for electrochemical detection are highly attractive. Herein, a meso-tetra(4-sulfonatophenyl)porphyrin silver/Ag nanoparticles/graphene phase C₃N₄ nanosheets (Ag₂TPPS₄/AgNPs/ng-C₃N₄) material with a sandwich-like structure was synthesized using a two-step photocatalytic reaction at room temperature (25 °C). In the first visible light irradiation step and in the presence of a hole capture agent, Ag⁺ ions were photocatalytically reduced onto the surface of ng-C₃N₄ that was used as a photocatalyst. Then, the protons (H⁺) in the core of H₂TPPS₄ were substituted in situ by photo-oxidized Ag⁺ during the second visible light irradiation step and in the presence of an electron capture agent. The electrochemical response of Ag₂TPPS₄ and ng-C₃N₄ to ractopamine (RAC) results in the unique double-faced active centers of Ag₂TPPS₄/AgNPs/ng-C₃N₄, and the cores (AgNPs) are beneficial as bridges for the connection between Ag₂TPPS₄ and ng-C₃N₄ and for high-efficiency electron transfer. Hence, as-synthesized Ag₂TPPS₄/AgNPs/ng-C₃N₄ exhibits high sensitivity (a low detection limit of 5.1 × 10^-8 M, S/N = 3.0), a wide linear range (1 × 10^-7 to 1.2 × 10^-5 M), and long-term stability. Based on the experimental verification of the electrochemical dynamics and electrostatic attraction at the interface between the dual-active-center surface and RAC, the electrochemical mechanism has been clarified. Specifically, in the multi-cycle oxidation of RAC, the blue shift of specific UV-vis peaks also confirms the electrocatalytic oxidation of the two terminal hydroxyl groups of RAC. In brief, Ag₂TPPS₄/AgNPs/ng-C₃N₄ with a sandwich-like structure and double-faced active centers enhances the detection sensitivity and electrocatalytic efficiency towards RAC.

MOF-derived core/shell C-TiO2/CoTiO3 type II heterojunction for efficient photocatalytic removal of antibiotics

A novel core/shell C-TiO₂/CoTiO₃ type II heterojunction was successfully synthesized via a direct calcination method by using MIL-125/Co core-shell nanocakes as a sacrificial template and precursor. In the calcination process, the organic ligand in MIL-125 acts as an in-situ carbon doping source to form a carbon-doped TiO₂ core (C-TiO₂). At the same time, CoTiO₃ nanoparticles are formed on the surface of C-TiO₂ by an in-situ solid-state reaction between the C-TiO₂ and Co²⁺ shell of MIL-125/Co. Due to such delicate core/shell structural features, carbon doping and type II heterojunctions, C-TiO₂/CoTiO₃ core/shell composites can effectively harvest visible light, facilitate the interfacial separation and suppress the recombination of photogenerated electron-hole pairs, leading to the remarkable photocatalytic activity for removal of ciprofloxacin (CIP). In particular, C-TiO₂/CoTiO₃-3 exhibits the best photocatalytic degradation activity of CIP with a degradation efficiency of 99.6% and a total carbon content removal percentage of 76% under visible-light illumination for 120 min. In addition, the proposed photocatalytic mechanism study illustrated that the main radical species in the photocatalytic degradation of CIP using C-TiO₂/CoTiO₃ as the photocatalyst is •OH. This work provides a new approach and insight for synthesizing core/shell heterojunction-based photocatalysts for various applications.