Citation: Ulfa, M.; Al Afif, H.; Saraswati, T.E.; Bahruji, H. Fast Removal of Methylene Blue via Adsorption-Photodegradation on TiO 2 /SBA-15 Synthesized by Slow Calcination. Materials 2022, 15, 5471. https://doi.org/10.3390/ ma15165471 Academic Editors: Won San Choi and Elza Bontempi Received: 24 June 2022 Accepted: 29 July 2022 Published: 9 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Fast Removal of Methylene Blue via Adsorption-Photodegradation on TiO 2 /SBA-15 Synthesized by Slow Calcination Maria Ulfa 1, * , Hafid Al Afif 1 , Teguh Endah Saraswati 2 and Hasliza Bahruji 3 1 Study Program of Chemistry Education, Faculty of Teacher Training and Education, Sebelas Maret University, Jl. Ir. Sutami 36A, Surakarta 57126, Indonesia 2 Faculty of Science, Sebelas Maret University, Jl. Ir. Sutami 36A, Surakarta 57126, Indonesia 3 Centre of Advanced Material and Energy Sciences, University Brunei Darussalam, Jalan Tungku Link, Darussalam BE1410, Brunei * Correspondence: ulfa.maria2015@gmail.com or mariaulfa@staff.uns.ac.id Abstract: TiO 2 /SBA-15 photocatalysts were successfully prepared by impregnating low loading titania to SBA-15 via slow calcination. The photocatalyst is efficient for fast methylene blue removal via adsorption and photodegradation methods. The impregnation of low TiO 2 loading via slow calcination enhanced TiO 2 dispersion that preserved the SBA-15 porosity and uniform morphology. High interfacial interaction of TiO 2 /SBA-15 improves TiO 2 photoresponse by narrowing the bandgap, resulting in a stronger redox ability. The methylene blue removal on 10%TiO 2 /SBA-15 followed the pseudo-second-order kinetic model that reached 67% removal efficiency in 90 min. The synergy between adsorption and photodegradation is responsible for the fast methylene blue removal. These results indicate the importance of maintaining the adsorption capacity in SBA-15 after impregnation with TiO 2 for efficient adsorption-photodegradation processes, which can be achieved by controlling the deposition of TiO 2 on SBA-15. A low titania loading further reduced the cost of photocatalysts, thus becoming a potential material for environmental pollution treatment. Keywords: SBA-15; TiO 2 ; slow calcination; low loading; adsorption-photodegradation 1. Introduction The rapidly growing textile industry increased the accumulation of dye pollutants such as methylene blue (C 16 H 18 ClN 3 S), which is harmful to the environment [1]. The threshold value for methylene blue in the water is about 5–10 mg/L, thus requiring the development of an efficient method for removing methylene blue waste [2]. Cheap and effective photocatalysts are continuously being investigated to obtain high efficiency and the fast removal of contamination in water [1,3]. One of the developments in dye treatment is via the combination of adsorption-photodegradation processes [4,5]. Several studies reported using SBA-15 and silica combined with carbon nitride or titania as an efficient photocatalyst for dye removal [4,6–9]. The method offers simultaneous adsorption of pollu- tants followed by photodegradation under light irradiation to decompose the adsorbed pollutants into less harmful molecules [6]. These two processes require synergy between the large surface area adsorbent for high accessibility of large dye molecules with the active photocatalysts for degradation [4,10]. TiO 2 is the most studied photoactive material that can be modified to produce various crystalline phases, structures, and sizes. TiO 2 is also very active under UV irradiation to catalyze redox reactions [11–14]. However, TiO 2 particles are easy to agglomerate, which limits their photodegradation usage. Hence, various methods are employed to increase TiO 2 stability, such as via the production of nanoparticles and deposition onto high surface area support [15,16]. Deposition of TiO 2 on Santa Barbara Amorphous-15 (SBA-15) mesoporous silica is a promising way to enhance photocatalytic activity [17–20]. SBA-15 has a large surface area of 400–800 m 2 /g, large pore diameter with structural regularity, high thermal-physical Materials 2022, 15, 5471. https://doi.org/10.3390/ma15165471 https://www.mdpi.com/journal/materials