Silica waste from the geothermal plant in Dieng-Indonesia can be utilized as amorphous silica source regarding the high content of silica and high productivity in the plant. However, in the presence of metal oxides, a series of purification steps need to be carried out. This paper describes silica xerogels preparation via acid leaching and sol gel method. Sulfuric acid was chosen in acid leaching due to corrosivity and safety factors. In the beginning, FTIR spectrophotometry and BET-BJH of geothermal silica revealed characteristic functional groups and physisorption of amorphous silica. Response data were collected based on XRF data to obtain silica content at optimum sulfuric acid concentration. To ensure the optimum data, it was confirmed by using XRF at prior and post leaching. The result informed that acid leaching attained optimum at 25% of acid concentration with R2 = 1 releasing more than 98% of silica. Leached silica was introduced a sol-gel method by using NaOH 2 N with a ratio of SiO2 to NaOH (1:6 (w/V)) followed 1 N of HCl addition. The product was aged for 18 h before washing and drying at 105 °C. The functional groups spectra such as hydroxyl (-OH), silanol (Si-OH), and siloxane (Si-O-Si) account for the molecular model that might be formed along with the polymerization process. Analysis of SEM and FTIR confirmed morphology, particle size, and disappearance of organic functional groups during the xerogel synthesis process from geothermal silica.

Glass coating films have been developed by many researchers in recent years. However, mass commercialization of this technology is still inefficient, and optimal methods are needed to produce affordable products. This paper introduces a film preparation method through, which a coating film is superimposed on silica glass by utilizing geothermal waste, a byproduct of geothermal power plants. Geothermal waste has been used as a silica precursor and modified using several silylation agents such as methyltriethoxysilane (MTMS), hexamethyldisilazane (HMDS), polydimethylsiloxane (PDMS), and surface-active agent (surfactant) cethyltrimethylammoniumbromide (CTAB). Design Expert 8.0.6 is used for optimization to find the desired product at the concentration of specific precursors and silane agents using contact angle responses. A model that consists of statistically significant variables can be generalized to a broad data range. The results of this study indicate that the glass surface coated with modified silica produces hydrophobic glass with contact angles up to 90° using the MTMS silylation agent.

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In recent years, there has been an increasing research interest regarding the development of superhydrophobic coating for various purposes with tetraethyl orthosilicate (TEOS) as the source of silica. Unfortunately, TEOS is hazardous as an alkoxide and need long step as well as time consuming to synthesize it. Typically, previous researches using fluoroalkylsilane (FOK) as the surface modification agent is containing fluoro compound which is not safety to use. This paper is aimed to develop a cost-effective and environmental-friendly superhydrophobic coating by utilizing bamboo leaf silica. This work was particularly conducted to develop the method of purification of bamboo leaf ash as the source of silica to produce superhydrophobic coating material. This method could be an effective and efficient way of preparing a superhydrophobic coating using silica bamboo leaf with eco-friendly solvent exchange agents. This observation used n-hexane, cyclohexane, isooctane as a solvent exchange, and trimethylchlorosilane (TMCS) as a surface modification agent which is not containing fluoro component. The initial bamboo leaf silica and purified silica were examined using XRD, BET, XRF, and SEM EDX Mapping to obtain essential information such as structure, porosity, purity, and surface topography. Also, the coated zinc plat with different solvents was assessed hydrophobicity by contact angle measurement and surface morphology by SEM. The efficient and effective formulation of the superhydrophobic coating was attained by applying n-hexane solvent, 13 %-v/v TMCS, 1.75 %-w/v of bamboo leaf silica was the highest of contact angle.