Cobalt orthosilicate (Co2SiO4) nanostructures and nanocomposites were successfully synthesized via a sol–gel method, by controlling different conditions. The gels were prepared starting from cobalt (II) acetatete tetrahydrate (Co(CH3COO)2·4H2O), tetraethyl orthosilicate, NH3 and carbohydrate at calcination temperature 500–700 °C for 5 h. We choose 700 °C as optimum calcination temperature base on XRD results. SEM images showed that NH3 and glucose are optimum catalysis and capping agent, respectively, in our experimental conditions. For the first time, glucose, fructose, sucrose, maltose and lactose were applied as capping agents to green synthesis of cobalt orthosilicates. The optical and magnetic properties of Co2SiO4 nanostructures were investigated by UV–Vis and VSM, respectively. Also, for the first time photocatalytic behavior of these nanostructures was evaluated using UV–Vis and degradation of methyl orange, methylene blue, erythrosine and eosine. DSC and TG curves of the nanocomposites showed both thermal stability and flame retardant property for Co2SiO4 nanocomposites prepared in the presence of the PS and PSU.