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.

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

Quick recombination of photogenerated electrons and holes in photocatalytic process remains a huge challenge. And the routine efforts are concentrated on heterojunction, metal decoration and surface defect strategies. PbTiO3 as a typical perovskite ferroelectrics is with a strong built-inelectric field as self-junction caused by internal spontaneous polarization, facilitating the charge separation in the photocatalytic process. Here, under UV irradiation, L-shaped PbTiO3 with active (1 1 0) facet as a photocatalyst was applied to photo-reduce graphene oxide (GO), where a specific reduced graphene oxide (rGO)/PbTiO3 composite was synthesized in presence of isopropanol, a hole-trapping agent. According to the linear optical properties, the polarizability of PbTiO3 is calculated to 1.01 × 10-23 cm3 (2.68 times that of P25 (TiO2)), inducing the photo-excited charge separation by PbTiO3. Based on XPS characterization, a TiOC chemical bond is identified on the interface between rGO and PbTiO3. The response peak current for an electrochemical sensor based on rGO/PbTiO3 was proportional to the concentration of pyrrole (6.6 × 10-9-3.1 × 10-7 M, R2 = 0.999), and an extremely low limit reaches to 2.38 × 10-9 M. In addition, polypyrrole during the pyrrole detection was realized by the multi-cycle oxidation process. And also, the electrochemical detection has been successfully applied for the pyrrole quantification in real samples.