Photocatalytic Hydrogen Evolution from Artificial Seawater Splitting over Amorphous Carbon Nitride: Optimization and Process Parameters Study via Response Surface Modeling

Photocatalytic water splitting has garnered tremendous attention for its capability to produce clean and renewable H-2 fuel from inexhaustible solar energy. Until now, most research has focused on scarce pure water as the source of H-2, which is not consistent with the concept of sustainable energy. Hence, the importance of photocatalytic splitting of abundant seawater in alleviating the issue of pure water shortages. However, seawater contains a wide variety of ionic components which have unknown effects on photocatalytic H-2 production. This work investigates photocatalytic seawater splitting conditions using environmentally friendly amorphous carbon nitride (ACN) as the photocatalyst. The individual effects of catalyst loading (X-1), sacrificial reagent concentration (X-2), salinity (X-3), and their interactive effects were studied via the Box-Behnken design in response surface modeling towards the H-2 evolution reaction (HER) from photocatalytic artificial seawater splitting. A second-order polynomial regression model is predicted from experimental data where the variance analysis of the regressions shows that the linear term (X-1, X-2), the two-way interaction term X1X2, and all the quadratic terms (X-12, X-22, X-23) pose significant effects towards the response of the HER rate. Numerical optimization suggests that the highest HER rate is 7.16 mu mol/h, achievable by dosing 2.55 g/L of ACN in 45.06 g sea salt/L aqueous solution containing 17.46 vol% of triethanolamine. Based on the outcome of our findings, an apparent effect of salt ions on the adsorption behavior of the photocatalyst in seawater splitting with a sacrificial reagent has been postulated.