Tdx 01

During the incubation, six bottles from the treatment group and two bottles from the control group were randomly selected at each time point of (0, 1, 3, 10, 17, 23, and 30) days. The headspace in each jar was sampled with a 500 μL syringe (Part Number/REF: 81256, HAMILTON, Romania) after vigorously shaking to remove the gas bubbles trapped in the sediment slurry. The concentrations of H₂, CO₂, and CH₄ in the headspace were measured on a gas chromatograph equipped with a packed column TDX-01 (Techcomp, Shanghai, China), a flame ionization detector (FID), and a thermal conductivity detector (TCD). The gas concentration was calibrated using H₂, CH₄, and CO₂ standards purchased from the National Institute of Metrology P. R. China Standard Gas Testing Center. The bottles were sacrificed after gas measurement. A pH meter (METTLER TOLEDO FE20, Shanghai, China) was used to measure the pH of the slurry.

To investigate the photocatalytic activity for hydrogen evolution, gas–solid static experiments using the same setup were conducted in consideration of poor solubility of methane in water. In short, 20 mg of photocatalyst was strewed in a glass dish, which was placed in a water bath of 25 mL deionized water, then the reactor was evacuated by a calibrated gas mixture of 10% methane in nitrogen and sealed with rubber septum. After illumination for 2 h, the amount of hydrogen was determined by a Techcomp GC7890II gas chromatographer with a Molecular Sieve 5A 80/100 Mesh column and a thermal conductivity detector. Other gas phase products and the liquid composition were analyzed by a Techcomp GC7900 gas chromatographer with TDX-01, TM-Al₂O₃/S and SE-54 columns, and flame ionization detectors.

Gases (methane and carbon dioxide) accumulated in the head space were periodically analyzed. 0.5 mL of gas was taken from the vial head space with a gastight syringe and directly injected into a gas chromatography (Techcomp, GC7900, China) with a thermal conductivity detector (TCD) and a stainless steel column (TDX-01, 4 mm × 2 m). Helium gas was used as the carrier gas with a flow rate of 30 mL min⁻¹. The oven was set at 100 °C and the injector and detector were maintained at 100 and 120 °C, respectively. Standard curves of each measured gas were established by injecting a known volume of high purity standard gas into the GC.