## 6 Conclusions  
Agricultural waste, in general, is less harmful than industrial waste. However, agricultural waste is disposed of in many forms, including burning which is commonly used to reduce the size of the waste. Since it produces GHG, it is vital to investigate ways to use such waste in a sustainable manner. The production of very pure nano-silica powder from rice husk, barley husk, barley grass, and wheatgrass is highlighted in the review. Various techniques were used, all with the objective of achieving a sustainable synthesis process to produce nano-silica, as well as meeting the target of waste eradication. To evaluate the synthesized silica nanoparticles, multiple characterization methods were utilized to establish the chemical composition, size, and shape. The significance of the numerous studies was their use of agricultural waste products as precursor raw materials. Acid reflux and heat management techniques were used to create magnetic micro-silica particles from wheat husk byproducts. Reflux and heat-treatment techniques were used to make nano-silica and nano-zeolite from wheatgrass. For the synthesis of nano-silica from barley and wheatgrass, processes based on green chemistry sustainable techniques were utilized, while for the synthesis of nano-silica from rice husk, an acid-leaching approach was used. Using the procedures outlined in this paper, it is feasible to successfully synthesize high-purity silica nanoparticles. The nanoparticles produced for this investigation were used for contaminant uptake, especially in aquatic environments. Diesel, petrol, and heavy metals, such as nickel, were studied as the pollutants, with a removal efficiency between 85 and 90%. Additionally, the research showed that the silica nanoparticles were reusable even after four cycles, and SNPs fabricated using wheatgrass showed a 10% reduction after the fourth use. The results showed that the nanoparticles being used as adsorbents were quite successful in removing a considerable percentage of pollutants. Since the nano-sorbents were synthesized from waste products of plants and agricultural materials, our research objectives were clearly achieved which were to study the sustainable impact of SNPs using green synthesis and for a greener environment. An assessment of the effectiveness of nanoparticles for reuse was an important component of the study and the results indicated an average cycle of four reuses was observed for all nanoparticles. Although an economic analysis of translating the synthesis process to commercial production is beyond the scope of the current investigation, it is vital, and the authors intend to conduct a value proposition and economic feasibility assessment in our ongoing studies.  
Conceptualization, D.K., E.A. and A.V.; methodology, D.K. and E.A.; software, D.K.; validation, D.K. and E.A.; formal analysis, E.A.; investigation, D.K, E.A.; resources, D.K.; data curation, D.K.; writing--original draft preparation, D.K., E.A. and A.V.; writing--review and editing, D.K. and A.V.; visualization, D.K.; supervision, D.K.; project administration, D.K.; funding acquisition, D.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding.  
Not applicable.  
The datasets generated and/or analyzed during the current investigation are available from the corresponding author upon reasonable request.  
The authors declare no conflict of interest.