I. N. Simpen, I. N. S. Winaya, I. D. G. A. Subagia, and I. W. B. Suyasa, “Green Nano-Composite of CaO/K-Sulfated TiO2 and Its Potential as a Single-Step Reaction Solid Catalyst for Biofuel Production”, KLS, vol. 7, no. 3, pp. 382–392, Jun. 2022.