Variation of annealing temperature with excess of NaOH concentration on Ag2S synthesis from argentometry titration waste as NTC thermistor

Utilization of AgCl from argentometric titration waste can be done by converting AgCl into silver sulfide (Ag2S) semiconductor. The variation of annealing temperature in Ag2S synthesis affects the properties and quality of the Ag2S semiconductor. Silver sulfide semiconductor can be applied as a NTC (negative temperature-coefficient) thermistor temperature sensor. The NTC thermistor shows a decrease in resistance with increasing temperature. This study aims to synthesize Ag2S from argentometric titration waste with excess NaOH concentration and variations in annealing temperature as a temperature sensor for NTC thermistors. Ag2S was synthesized using thiourea reagent in alkaline NaOH medium. The synthesized silver sulfide was then annealed at various temperatures of 100, 200 and 300 °C for 30 min. Ag2S was then characterized using Thermo Gravimetrical Analysis (TGA), X-Ray Diffraction (XRD) and UV–Vis Diffuse Reflectance Spectroscopy (UV–Vis DRS). The results of TGA analysis showed that Ag2S at a temperature of 836 °C had decomposed into Ag and S2. From the XRD characterization results showed the presence of Ag2S at 2θ peaks of 22; 29; 31; 38 and 41°. Ag2S crystal size increases with increasing annealing temperature, which are 37.04; 39.55 and 41.68 nm. The results of UV–Vis DRS characterization showed that the Ag2S band gap value decreased with increasing annealing temperature, which were 0.96; 0.94; and 0.92 eV. The resistance measurement results show that the Ag2S semiconductor at annealing temperature of 300 °C is an NTC thermistor with good electrical quality, has a sensitivity of 6.85% and a thermistor constant of 6087 K.