Efficient hydrogen peroxide photogeneration over GaOOH/In(OH)3 composites via the half-reaction of tetracycline oxidation

Material Characterization: The phase state and crystal structure of GaOOH/In(OH)3 composites were observed by X-ray diffraction (XRD, PANalytical X’ pert powder). The morphology and size of obtained samples were imaged by scanning electron microscopy (SEM, Hitachi SU8000), transmission electron microscopy (TEM, JEOL JEM-F200). The specific surface area of samples was observed by nitrogen adsorption with a TriStar II Plus 3.03 instrument. UV–vis diffuse reflectance spectra and photoluminescence (PL) spectra were recorded by a UV 3600 UV–vis spectrometer and a FLS1000 transient steady-state fluorescence spectrometer respectively. Electron spin resonance (ESR) spectra were obtained by a Bruker model A300-10/12 with TEMPO as spin trapping agent. The elemental composition of samples was analyzed by X-ray photoelectron spectroscopy (XPS, Thermo escalab 250XI). EIS electrochemistry workstation (CHI760E, Shanghia Zhenhua Tech. Co., Ltd., China) at room temperature. 20 mg powder sample was dispersed into 500 μL Nafion and 500 μL of water under ultrasonication for 30 min. The as-prepared samples coated on an ITO glass acted as the working electrode with an active area of 1 cm2, whereas a Pt wire and calomel electrode were used as the counter and reference electrode respectively. 50 mL 0.5 M Na2SO4 aqueous solution was selected as the electrolyte.Computational details: Density functional theory (DFT) calculations were using the Cambridge Serial Total Energy Package (CASTEP) module. Generalized gradient approximation (GGA) with the Perdew-Burke Ernzerhof (PBE) function was selected to study the exchange-correlation interaction. The sampling of the Brillouin zone was conducted using a 3 × 4 × 1 k-point grid for GaOOH. The sampling of the Brillouin zone was conducted using a 2 × 2 × 1 k-point grid for In(OOH)3.and The sampling of the Brillouin zone was conducted using a 1 × 2 × 1 k-point grid for GaOOH/In(OOH)3. To assure rigorous consistency, calculations were performed until the energy convergence threshold was less than 10-5 eV. To effectively isolate periodic structures and preclude their interaction, a vacuum buffer of 15 Å was inserted along the z-axis. The unit cell of GaOOH is defined by the lattice constants: a = 9.77900 Å, b = 5.93200 Å, and c = 22.23640 Å. α=β=γ= 90°; The unit cell of In(OOH)3 is defined by the lattice constants: a = 15.94860 Å, b = 11.27740 Å, and c = 23.51440 Å. α=β=γ= 90°; The unit cell of In(OOH)3 is defined by the lattice constants: a = 18.00000 Å, b = 11.57070 Å, and c = 25.14290 Å. α=β=γ= 90°.Section 3:The DPD-POD colorimetric method was used to measure the H2O2 content. N,N-diethyl-phenylenediamine and horseradish peroxidase were the chromogenic agents respectively, and the buffer was 0.1M phosphate solution.Preparation of chromogenic agents: 0.1 g DPD dissolved in 10 mL 0.1 M H2SO4 solution to obtain 10 mg mL-1 DPD solution. 0.01 g POD dissolved in 10 mL deionized water to obtain 1mg mL-1 POD solution. Store both solutions at 4℃ for one week.Preparation of phosphate solution: 99.7 mL deionized water, 87.7 mL 1M sodium dihydrogen phosphate solution, 12.6 mL disodium hydrogen phosphate solution mixed.Detection procedures: The 1 mL sample was added with 0.4 mL phosphate buffer, 1.12 mL deionized water, 50 μL DPD solution and 50 μL POD solution, mixed evenly and poured into a colorimetric dish. The absorbance of the solution was measured at 551 nm wavelength. Since the DPD solution is easily oxidized, the detection process is completed within 6 minutes after adding the chromogenic agents.