. 2022 Jun 23;12(29):18524–18546. doi: 10.1039/d2ra02747j

Physical characteristics of nanostructured silica synthesized from biogenic sources.

Sl. No.	Biogenic precursor	BET surface area (m² g⁻¹)	Particle size (nm)	Pore size (nm) and pore volume (cm³ g⁻¹)	Method	Ref.
1	Palm oil mill fly ash	pH 8.75 to 8.30: 140.75 to 79.91	10.67 ± 1.44 μm	—	Sol gel precipitation	62
		pH 9.5; RT to 95 °C: 50–140			Gel destabilization by CO₂
		pH 9.5; RT to 95 °C: 50–140			Mechanical defragmentation of SiO₂ cake
2	Barley grain waste	Acid treated barley, 700 °C: 323	∼150	Pore size: 22	Waste washed, dried and dried powdered into fine particles	63
				Pore volume: 1.045	Fine particles powdered boiled in HNO₃, rinsed with distilled water, and dried
					Dried sample refluxed with HCl after which apportioned into four lots and heated at 400, 500, 600, 700 °C
3	Sugarcane waste ash	131	<20	—	Ash pretreatment with acid, washing and sieving	64
					Formation of Na₂SiO₃ at 400 °C
					Co-condensation to form SiO₂ NPs using H₂SO₄
					Surfactant: CTAB
4	Rice husk	—	Ball Milled 18 to 36 h: <3 μm	—	RH washing, drying and burning at up to 700 °C	65
			Ball milled 72 h: < 1 μm		Acid leaching using H₂SO₄, HNO₃ or HCl, washing, filtration and drying to powder
					Ball milling of powder
5	Rice husk ash	Thermal treatment at 700 °C: 1 to 3 h: ∼2.83 to 2.74 at 800 °C: 1 to 3 h: ∼1.70 to 1.46	Thermal treatment at 700 °C: 1 to 3 h: ∼17.72 to 18.53 at 800 °C: 1 to 3 h: ∼22.55 to 22.78	—	Different methods	17
		Acid leach: ∼2.97	Acid leach: ∼20.10		Thermal treatment of RHA with no pretreatment at 700 °C and 800 °C for 1, 2, and 3 h
		Alkali: ∼290.03	Alkali: ∼205.10		Acid leaching and drying
					- Heating treatment at 800 °C
					Extraction in boiling NaOH and precipitation by HCl at low temperature
6	Wheat husk	513 to 587	—	Pore size: 9–15	Acid leaching with HCl; calcination at 600 °C	66
				Pore volume 2.3–4.0	Boiling with NaOH to Na₂SiO₃
					Resin-exchange-alkali-catalysis following solvent exchange, surface modification, and drying
7	Equisetum arvenses	Acid wash 1; 2, pH 7: No calcination: ∼74.08; 83.45 &773 K: ∼74.08; ∼330.63; 823 K: ∼296.40; 296.40; 873 K: ∼274.64 to; 250.73	Acid wash 1; 2, pH 7: No calcination 36.65; 32.54; 773 K: 9.16; 8.21; 823 K: 9.89; 9.16; 873 K: 11.77; 10.83	—	Calcination	67
		Acid wash 2, pH 4: No calcination: ∼69.57; 773 K: ∼250.49; 823 K: ∼228.03; 873 K: ∼216.91	Acid wash 2, pH 4: No calcination; 39.03; 773 K: 10.84; 823 K: 11.91; 873 K: 12.52		- Water and acid washing under pressure at 393 K
					- Drying at 376 K
					- Ball milling to 10 to 20 mm
					- Calcination at 773 K, 823, K and 873 K
8	Teff Straw	—	Amorphous silica (50 nm)	—	- Thermo-chemical treatment Sol–gel process	68
8	Teff Straw	—	Amorphous silica (50 nm)	—	- Increased SiO₂ concentration ≈ 92% ashes at 600 °C & an acid treatment ≈99%	68