The semiconductor NiS₂ nanoparticles with an average size of 10 ± 0.317 nm were successfully deposited on the reduced graphene oxide (rGO) sheets by simple hydrothermal method. The synthesized nanocomposite was characterized by various instrumental techniques like XRD, FTIR, FESEM, EDX, HRTEM, fluorescence spectrophotometer analysis. In this study we mainly focus on the determination of the surface potential values of NiS₂-rGO and CoS-rGO nanocomposite under different experimental conditions and evaluated the photodegradation efficiency towards azo dye Congo Red (CR) molecule under natural sunlight irradiation. We found that the surface charge (zeta potential) of the both nanocomposite materials in presence of different inorganic ions salt solutions like NaCl, NaNO₃, Na₂SO₄, MgCl₂, CaCl₂ etc. is varied based on the polarizability of the ions as well as pH of the suspension. Different inorganic ions present in the catalyst suspension can alter the surface charge of the catalyst by forming a double layer around the molecule and thus change the electrostatic interaction between the dye molecule and the catalyst surface which change the degradation efficiency of the photocatalyst towards CR molecule. The photocatalytic efficiency of NiS₂-rGO and CoS-rGO nanocomposite towards CR degradation was found to be 97.03% and 88.03% in 40 min, respectively under same experimental condition whereas NiS₂ and CoS nanoparticles without support exhibited photodegradation efficiency 57.89% and 50.52%, respectively. The observed improved photocatalytic activity of the metal sulfide-rGO nanocomposite results the presence of synergistic effect between the metal sulfide nanoparticles and the rGO sheets of the photocatalysts which inhibits the recombination rate of photogenerated electrons and holes. The mechanism of the degradation process was investigated by photoluminescence study in presence of terephthalic acid and also quenching experiment in presence of isopropanol and benzoquinone. The photocatalyst was characterized after degradation process and found that the crystallinity and the morphology of the nanocomposite remained unchanged. The ion-chromatography experiment confirms the formation of non-toxic products after degradation. The present study focuses on the importance of the use of metal sulphide-rGO nanocomposite towards environment remediation process and study of the influence of inorganic salts on the surface charge of the photocatalyst as well as on the degradation process.

通过简单的水热法将平均尺寸为10±0.317 nm的半导体NiS ₂纳米颗粒成功沉积在还原的氧化石墨烯（rGO）板上。合成的纳米复合材料通过XRD，FTIR，FESEM，EDX，HRTEM，荧光分光光度计分析等多种仪器技术进行了表征。在这项研究中，我们主要致力于在不同的实验条件下测定NiS ₂ -rGO和CoS-rGO纳米复合材料的表面电势值，并评估在自然阳光照射下对偶氮染料刚果红（CR）分子的光降解效率。我们发现，在不同的无机离子盐溶液（如NaCl，NaNO _3）存在下，两种纳米复合材料的表面电荷（ζ电位）Na ₂ SO ₄，MgCl ₂，CaCl ₂等根据离子的极化性以及悬浮液的pH而变化。催化剂悬浮液中存在的不同无机离子可通过在分子周围形成双层来改变催化剂的表面电荷，从而改变染料分子与催化剂表面之间的静电相互作用，从而改变光催化剂对CR分子的降解效率。的NiS的光催化效率₂ -rGO并且朝向CR降解COS-RGO纳米复合材料被认为是97.03％，在40分钟88.03％，分别相同的实验条件，而下的NiS ₂无载体的CoS纳米颗粒和CoS纳米颗粒的光降解效率分别为57.89％和50.52％。观察到的金属硫化物-rGO纳米复合材料改善的光催化活性导致金属硫化物纳米粒子与光催化剂的rGO片之间存在协同效应，从而抑制了光生电子和空穴的复合速率。通过在对苯二甲酸存在下的光致发光研究，以及在异丙醇和苯醌存在下的猝灭实验，研究了降解过程的机理。降解过程后对光催化剂进行了表征，发现纳米复合材料的结晶度和形态保持不变。离子色谱实验确认了降解后无毒产物的形成。