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Silica nanoparticles (SiNPs) have shown a wide range of applications in various technological fields. It is due to their unique properties such as biocompatibility, stability, tunable pore size, high surface area and surface reactivity. The ease of surface functionalization of SiNPs further extends their applications in biomedicine, targeted drug delivery and biosensing applications. Most of the works on SiNPs are focused on their synthesis by chemical methods for different applications. However, SiNPs can be prepared by green synthetic protocols that utilize plants, agriculture waste, industrial waste, fungi, bacteria, yeast, clay/mineral, worms, actinomycetes, etc. The green and sustainable methods offer distinctive encouraging features to produce nanomaterials with desired properties. The green synthesis of silica nanoparticles is an important area of research having considerable potential for further future developments. In this mini review, collective information on current green approaches for the synthesis of SiNPs is presented. The various green methods of synthesis for SiNPs are discussed with examples from the literature. The future challenges and expected advances are also pointed out which will decide the direction of research in this field.

Silica and silica based hybrid nanoparticles are investigated with great interest for the removal of dyes from water. The presence of surface silanols which can complex the dyes, ease of grafting of additional functionalities to improve the complexation, the possibility of photocatalyst grafting for dye degradation and good chemical stability are the reasons for the excellent efficiency of silica nanoparticles to remove dyes from water. In this overview the main strategies used for the removal of dyes from water by using silica nanoparticles are discussed. The use of bare, core-shell and polymer-grafted silica nanoparticles for removal of dyes is explained with examples. Additionally, very latest reports about the synthesis and use of silica and hybrid silica nanoparticles for removal of dyes from water are discussed and critically analyzed. The future challenges in the development and use of silica nanoparticle based technologies for removal of dyes are pointed out with explanation.