Table 1.

Commonly used materials for catalytic removal of VOCs.

No.	Catalytic	Category	VOC	Nanomaterial	Morphology	Medium	Doping Concentration	Synthesis	Ref.
1	Photo-	TiO2	Trichloro-ethylene	nanostructured TiO2 particles	Primary particle size: 2.3–30 nm, secondary particle size: 100–900 nm	titanium isopropoxide	water concentrations: 2.3, 0.3, 0.27, and 0.18 M	low-temperature synthesis, modified sol–gel method	[33]
2	Photo-	TiO2	Toluene	Titanium isopropoxide	Primary particle size:11 nm	isopropanol–water solution	2.5 mL H2O, 25 mL ethanol, 150-mL (hydrothermal)	sol–gel synthesis, thermal & hydrothermal methods	[34]
3	Photo-	TiO2	Toluene	TiO2 thin films	particle sizes less than 100 nm, monocrystalline nanodiamond	Titanium (IV) tetraisopropoxide (TTIP) (Ti(OCH(CH3)2)4) and water		detonation method (purchased from microdiamant)	[35]
4	Photo-	TiO2	Toluene, acetaldehyde	TiO2 nanotubes (TNT) & nanopartcles (TNP) film; commercial TiO2 (P25)	average surface area of 50 m2 g−1, primary particle size: 20–30 nm, channel pores diameter: 40–60 nm, tube length: 9.5 (±0.9) μm.	[TNP] Ethanol [TNT] ethylene glycol electrolyte	[TNP] 0.15 g/mL [TNT] 1st anodization: 0.5 wt% NH4F and 3 wt% H2O; 2nd: 0.3 wt% NH4F and 1 wt% H2O.	[TNP] doctor-blade method [TNT]two-step electrochemical anodization	[36]
5	Photo-	TiO2	Toluene	Ti-foil (99.7%,0.25 mm, Aldrich, USA)	top and bottom opened structure of which thediameters are 100 nm and 50 nm, respectively NP@DNT films of 15 (±2) μm	ethylene glycol solution containing 0.25 wt% NH4F and 0.3 vol% distilled water		potentiostatic anodization method	[37]
6	Photo-	TiO2	Hexane, methanol	anatase and rutile TiO2 (0.1 mol)	Surface area between 39 to 84 m2/g (given in table)	1.5 mol anhydrous Ethanol, water–ethanol solution containing 1 mol ethanol with a ratio of water:butoxide = 50:1.	aqueous HNO3 solution of various concentration (0.1–1.0 mol/L) with the ratio of solid (g): liquid (mL) = 1:10	hydrothermal method	[38]
7	Photo-	TiO2	Toluene	Anatase/brookite/rutile tricrystalline TiO2	amorphous TiO2 suspension	HNO3 solution (65%)	The molar ratios of HNO3 to TBOT (RHNO3) were varied from 0.2 to 1.2 at intervals of 0.2 by varying the volume of HNO3 solution.	low-temperature hydrothermal method	[39]
8	Photo-	TiO2	Toluene	co-alloying TiO2	fine bright yellow powder, primary particles diameter: 1–2 μm	TiCl4 reacted with NbCl5 and urea in an ethanol solution	toluene concentrations: 1~5 ppm; relative humidity: 25~65%; air velocity: 0.78~7.84 cm/s; irradiancy: 42~95 W/m2.	urea-glass synthesis	[40]
9	Photo-	TiO2	Isopropyl alcohol	Hybrid CuxO/TiO2 Nanocomposites	Commercial TiO2 (rutile phase, 15 nm grain size, 90 m2/g specific surface area)	CuCl2 solution, NaOH and glucose solutions (reduce & control the CuI/CuII ratio	10 mL of CuCl2 solution. Weight fraction of Cu: TiO2 is 1 × 103: 2 × 102.	simple impregnation method	[41]
10	Photo-	TiO2	Toluene	commercial TiO2 (P25)	Platinum nanoparticles in the size of 1–3 nm were clearly deposited on the surface of TiO2	0.5 wt% Pt and 30 mM fluoride for VOC degradation	sodium fluoride (10, 30, and 50 mM) and Pt (0.1, 0.5, and 1 wt%)	photo deposition method	[42]
11	Photo-	TiO2	Toluene	hybrid nanomaterial Pt-rGO-TiO2	TiO2 nanopowder: commercial P25 (Degussa).	ethanol-water	0.1, 0.5, 1 and 2 wt% Pt-rGO-TiO2 nanocomposite catalysts	solvothermal method	[43]
12	Photo-	TiO2	Toluene	Composites ACFF 0.5 mL tetra-butyl titanate (97 wt%)	Diameter: 12 μm, pore size: 32 μm.	Polytetrafluoroethylene (Teflon)-lined stainless-steel autoclaves	1.0, 2.0, 3.5 and 5.0 l of toluene were injected into the above reactor	Purchased ACFF,	[6]
13	Photo-	TiO2	Formaldehyde, trichloro-ethylene	TiO2 nanoparticles	BET area:392 m2 g−1, micro mean pore size: 0.6 nm	8 wt% DAPs		incipient wetness impregnation, freeze-drying, or mechanical mixing	[44]
14	Photo-	Zinc oxide	Toluene	ZnAl2O4 nanoparticles	commercial P25 powder (reference) TiO2 nanoballs in anatase phase	[solvothermal synthetic] Al(NO3)3·9H2O (2 mmol), Zn(NO3)2·6H2O (1 mmol), ethylene glycol (30 mL) [citrate precursors] 0.01 M Zn(NO3)2·6H2O, 0.02 M Al(NO3)3·9H2O, 100 mL DI water [hydrothermal] an equimolar amount of Zn(NO3)3·6H2O (2 mmol), Al(NO3)3·9H2O (4 mmol), urea[CO(NH2)2] (20 mmol) and deionized water (80 mL)		solvothermal, citrate precursor, hydrothermal methods	[45]
15	Photo-	Ni oxide	Toluene	Nitrogen-doped carbon nanotubes (NCNTs) supported NiO(NiO/NCNTs)	NCNTs: tubular structure, 20 nm-diameter; NiO: crystallite, 3–10 nm	catalyst and pyridine and/or 3-(aminomethyl)pyridine	volume ratio of pyridine to 3-(aminomethyl)pyridine: 5, 3, 1 and 0	Chemical vapor deposition method	[46]
16	Photo-	WO3	H2O2	Nano-diamonds combined with WO3	ND: ca. 4–6 nm diameter	WO3 (Aldrich)	0.5–16 wt% ND contents	Simple dehydration condensation	[47]
17	Photo-	Manganese Oxide	Benzene, Toluene, Ethylbenzene, Xylenes	Manganese Oxide and Copper	KMnO4 solution (OMS-2); Mn(CH3COO)2 4H2O (AMO)	Mn(CH3COO)2 solution (OMS-2); KMnO4 (AMO);		a simple refluxing method	[48]
18	Photo-	Manganese Oxide	Formaldehyde indoors	manganese oxide	Shown in SEM images	ethanol solution of manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O	Mn(CH3COO)2·4H2O:PAN-ACNF 0.5–20 wt.%		[49]
19	Photo-	Bi-based compounds	Acetone, toluene	Bi2WO6	CQDs: high dispersion, uniform size of 3–5 nm in diameter	carbon quantum dots (CQDs)	adding 1.0–6.0 g of CQDs	Hydrothermal synthesis	[50]
20	Photo-	AgBr	methyl orange	AgBr	monoclinic WO3 substrate, face-centered cubic AgBr nanoparticles: crystalline sizes less than 56.8 nm.	WO3	AgBr contents were respectively obtained and defined as TA-0.05, TB-0.10, TC-0.15, TD-0.20, TE-0.25, TF-0.30 and TG-0.40.	deposition–precipitation method	[51]
21	Thermal	Platinum	Toluene	Pt/Al2O3–CeO2 nanocatalysts	average size: 5–20 nm.	CeO2(10%)/Al2O3, 2.8 g Ce(NO3)3·6H2O, 100 mL distilled water	ceria loading of 10, 20 and 30%	wet impregnation method	[52]
22	Thermal	Platinum	benzene	Pt/Al2O3	Pt particle sizes between 1.2–2.2 nm	H2PtCl6·6H2O	Pt/A l2O3−x, x: pH value of 7.0, 9.0 and 11.0	modified ethylene glycol (EG) reduction approach	[53]
23	Thermal	Platinum	Formaldehyde (HCHO)	Pt/TiO2/Al2O3	BET area from 16.5 to 182.5 m2/g	(NH4)[TiO(C2O4)2]	The platinum loading: 0.62, 1.26,1.19 and 1.25 gm−2	Electro-deposition technology	[54]
24	Thermal	Silica-iridium	Toluene	chloride-ion free iridium acetylacetonate, Ir(AcAc)3	∼5 to 27 nm	SiO2 Degussa Aerosil 200	Size of iridium particles: ~5 to 27 nm (calcination temperature 350~750 °C)	incipient wetness impregnation	[55]
25	Thermal	Carbon	benzene, toluene, ethylbenzene, and oxylene	Pt/carbon nanotube (CNT) Multiwalled carbon nanotubes (MWCNT)	CNTs: 20–50 nm column diameters MWCNTs: 20–50 nm diameters	acid treatment using HF, H2SO4, and HNO3	Pt content in the catalysts ranging from 10 to 30 wt%.	a molecular-level mixing method	[56]
26	Photo-	Carbon based	Volatile Aromatic Pollutant	TiO2_graphene	Shown in SEM image	An ethanol-water solvent	P25_GR with weight addition ratios of 0.2, 0.5, 1, 2, 5, 10, and 30% GR.	facile hydrothermal reaction	[57]
27	Photo-	Carbon-based	methanol	graphene oxide, reduced graphene oxide, and few-layer graphene	BET area (m2/g): rGO+TiO2: 49.34, GO+TiO2: 43.79, G+TiO2: 41.54	Polyacrylonitrile	a polymer concentration of 5% (w/w) in N,N-dimethylformamide.	hydrothermal method (reduced graphene oxide); others purchased	[58]