Development of rice husk and coconut coir-based green desiccants toward industrial moisture control applications

Agricultural waste materials such as rice husk and coconut coir offer eco-friendly, low-cost alternatives to conventional desiccants. This study evaluates their potential for moisture control applications following nitric acid (4 N HNO₃) treatment. Scanning Electron Microscopy (SEM) revealed that acid treatment significantly increased porosity from 34.95% to 53.13% in rice husk and from 39.72% to 52.90% in coconut coir. Fourier Transform Infrared Spectroscopy (FTIR) confirmed enhanced hydroxyl group availability, with treated rice husk showing 1.61-fold higher O-H peak intensity compared to untreated samples. Thermogravimetric Analysis (TGA) demonstrated substantially lower regeneration temperatures: 150 °C for rice husk and 118 °C for coconut coir, compared to conventional desiccants (silica gel: 120-180 °C; zeolites: 200-400 °C). Moisture adsorption testing at 75% relative humidity showed treated rice husk achieved 48.2 g (100 g) -1 capacity while treated coconut coir reached 57.0 g (100 g) -1 , both exceeding silica gel (35-40 g (100 g) -1 Rice husk exhibited superior thermal stability (up to 542 °C) and durability, making it ideal for high-temperature industrial applications, while coconut coir demonstrated faster regeneration kinetics suitable for energy-efficient systems. A Figure of Merit integrating adsorption capacity, regeneration time, and temperature (0.321-0.322 g/100 g/h/°C) confirms their competitive performance. These findings establish that acid-treated agricultural waste is a viable, sustainable desiccant with promise for future industrial moisture control, air conditioning, and food preservation applications.