Adsorption efficiency and photocatalytic activity of silver sulphide-activated carbon (Ag2S-AC) composites

Background
This study investigates the adsorption efficiency and photocatalytic activity of silver sulphide-activated carbon (Ag2S-AC) composites derived from ground coffee waste (GCW).

Methods
In this work, GCW was preceding to carbonized at 500 ± 2°C for hours and formed biochar. Then, GCW was subjected to activation using hydrochloric acid (HCl), phosphoric acid (H3PO4) and potassium hydroxide (KOH). The mixture was left to soak for 24 h at room temperature, followed by carbonization at 350 and 500˚C. In the meantime, the silver sulphide (Ag2S) was synthesized by using an ion exchange method. Sodium sulphide (Na2S) was used as sulphur source and mixed with silver nitrate (AgNO3) and sodium citrate (NaCit) for two hours, then dried in oven at 50 ± 2°C for 10 h. Next, the carbonized AC was subsequently combined with synthesized silver sulphide, resulting in the creation of Ag2S-activated carbon composites that functioned both as adsorbent and photocatalyst. Their capabilities as adsorbents and photocatalyst were studied by using copper ions (Cu2+) and methylene blue (MB) solution.

Significance findings
Based on results, GCW and all the prepared activated carbons are in the amorphous phase, except for the Ag2S-AC composites, where the Ag2S peak reflection can be observed from the X-ray diffraction (XRD) pattern. GCW shows rough and dense surface morphology. The AC shows different pore sizes and structures depending on the chemical activators used, where AC-KOH shows the largest pore size (165.31 μm). The existence of micropores can be observed in all the activated carbon samples. For the adsorption of Cu2+, all samples show more than 99 % of the removal efficiency. While for photocatalytic testing, the Ag2S-H3PO4 sample shows the highest degradation rate (97.7 %) of MB solutions.