Wastewaters of the textile industry, e.g., those generated in Gresik, Indonesia, are a possible threat to the environment and should be treated before disposal. Photodegradation is a more promising method to overcome this problem than conventional methods such as biodegradation. ZnO is widely used for photodegradation due to its unique physical and chemical properties and stability. In this study, Ag was loaded onto ZnO, which is non-toxic and inexpensive, can improve the electron–hole separation, and has a significant catalytic potential. Pristine ZnO and ZnO-Ag nanoparticles were fabricated by an ultrasonic spray pyrolysis system at different Ag contents (1, 5, and 10 wt%). The carrier gas ratio (O2:N2) was also changed (1:0, 1:2, 1:1, 2:1, and 0:1) to examine its effects on the nanoparticle characteristics. The nanoparticle characteristics were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer, Emmett, and Teller (BET) specific surface area. The results were interpreted in relation to photodegradation under UV light irradiation. An increase in the ZnO-Ag activity compared with pristine ZnO was observed at a carrier gas ratio of 0:1 with reaction rate constants of 0.0059 and 0.0025 min−1, respectively.

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Modelling of the droplet formation and drying process in the synthesis of Zinc Oxide-Silicon Dioxide (ZnO-SiO2) composite have been conducted through a CFD modelling. In general, modelling of spray drying only focused on exploring the drying chamber section. The phenomenon builds in a consecutive electrospray and spray drying method has been successfully studied in this paper. The influence of carrier gas flow rate (2 to 10 L/min), precursor flow rate (1 to 10 ml/h), drying chamber temperature and applied voltage (12 to 14 kV) were investigated systematically. Numerical modelling was conducted to describe the mechanism of the composite droplet formation through the jet shape of the electrospray. Evaporation of the initial composite droplet was considered in the modelling, accounting for its size evolution. Simultaneous mass transfer modelling due to the composite evaporation was solved in combination with a general dynamic equation solution. The modelling results show that the applied voltage and the precursor flow rate effectively affected the composite droplet size. While the carrier gas flow rate and the drying chamber temperature, influenced the effectiveness of the composite particle formation in the spray drying synthesis.