This study investigates the effect of Ca²⁺ doping on the visible light photocatalytic degradation of 4-nitrophenol (4-NP) using AgInS₂ (AIS). The researchers synthesized AIS and Ca²⁺-doped AIS (Ca-AIS) using a low-temperature liquid phase method. Structural and optical properties of the materials were analyzed using SEM, XRD, XPS, HRTEM, BET, PL, and UV-Vis DRS. The results showed that doping with an appropriate amount of Ca²⁺ improves the visible light catalytic activity of AIS. Under visible light irradiation for 120 minutes, a degradation rate of 63.2% for 4-NP was achieved with 1% Ca-AIS. The study suggests that Ca²⁺ doping reduces the band gap and interface resistance of AIS, enhancing its photocatalytic performance. The mechanism involves the generation of reactive species such as ·OH and h⁺, which participate in the degradation of 4-NP. The study also highlights that excessive Ca²⁺ can hinder photocatalytic activity by promoting recombination of charge carriers. The findings indicate that Ca-AIS is a promising photocatalyst for degrading organic pollutants under visible light. The research provides insights into using cheap alkaline earth metals as dopants to enhance photocatalytic efficiency.This study investigates the effect of Ca²⁺ doping on the visible light photocatalytic degradation of 4-nitrophenol (4-NP) using AgInS₂ (AIS). The researchers synthesized AIS and Ca²⁺-doped AIS (Ca-AIS) using a low-temperature liquid phase method. Structural and optical properties of the materials were analyzed using SEM, XRD, XPS, HRTEM, BET, PL, and UV-Vis DRS. The results showed that doping with an appropriate amount of Ca²⁺ improves the visible light catalytic activity of AIS. Under visible light irradiation for 120 minutes, a degradation rate of 63.2% for 4-NP was achieved with 1% Ca-AIS. The study suggests that Ca²⁺ doping reduces the band gap and interface resistance of AIS, enhancing its photocatalytic performance. The mechanism involves the generation of reactive species such as ·OH and h⁺, which participate in the degradation of 4-NP. The study also highlights that excessive Ca²⁺ can hinder photocatalytic activity by promoting recombination of charge carriers. The findings indicate that Ca-AIS is a promising photocatalyst for degrading organic pollutants under visible light. The research provides insights into using cheap alkaline earth metals as dopants to enhance photocatalytic efficiency.