Mitigation of hazardous ammonia and hydrogen sulphide emissions using carbon based nanometal oxides adsorbents

Carbon based nano TiO₂-ZnO composite adsorbents were developed and evaluated for simultaneous adsorption of ammonia (NH₃) and hydrogen sulphide (H₂S). Screening of composites with different ZnO and TiO₂ loadings in terms of adsorption capacities identified a composite with 10% ZnO and 5% TiO₂ (10ZnO-5TiO₂-AC) as the most suitable. Breakthrough experiments with pre-mixed gases containing 50 to 550 mg L^− 1 of each NH₃ and H₂S at 22 to 280 °C showed that increase in NH₃ and H₂S concentrations led to higher equilibrium adsorption capacities for both gases. Increase of temperature decreased NH₃ equilibrium adsorption capacity but for H₂S higher values were observed at higher temperatures. The highest equilibrium adsorption capacity of 5.71 mg NH₃ g^− 1 was obtained with a mixture of 500 ppmv NH₃ and 550 ppmv H₂S at 22 °C, while for H₂S the highest value of 29.64 mg H₂S g^− 1 was seen with a mixture of 300 ppmv NH₃ and 300 ppmv H₂S at 280 °C. Multicomponent Langmuir isotherm described the simultaneous adsorption of NH₃ and H₂S with the high level of accuracy. The negative value of enthalpy of adsorption for NH₃ confirmed the exothermic and potentially physical nature of ammonia adsorption, while a positive value for H₂S adsorption pointed out to the endothermic and chemisorption nature of this process. Examination of fresh and exposed composite adsorbents by XRD and FTIR confirmed the chemical nature of H₂S adsorption.