Photocatalysis and Bandgap Engineering Using ZnO Nanocomposites

Table 1

Composites described here for light harvesting and photocatalytic activity.

Composite	Nanocomposite type	Year of publication	UV-Vis absorption range/edge (nm)	Reference	Remarks
ZnO/CdS	Nanospheres	August 2011	480	[148]
ZnO-CdS	Core-shell nanorods	August 2010	540	[150]
CdS@ZnO	Nanourchins	December 2012	512	[151]	Enhanced efficiency due to specific morphology which increased reactive area.
CdS-ZnO	CdS NPs on ZnO disk and CdS NPs on ZnO nanorods	August 2011	550	[153]	Metallic features of both polar surfaces provide more feasible path for charge transfer between ZnO and CdS, thus enhancing PC performance.
ZnO/CdS	ZnO/CdS core-shell nanorods	October 2012	480	[154]	CdS3 showed superior absorption; the photocatalytic efficiency was better due to ZnO and CdS3 favorable synergetic effect.
ZnO/CdS	Flower-like ZnO modified by CdS NPs	July 2011	500	[155]	ZnO/CdS nanoheterostructures exhibit superior PC activities due to increased photoresponding range and increased charge separation rate.
ZnO/CdS	CdS NPs/ZnO NWs	March 2009	550	[156]
ZnO-CdS@Cd	Rod-like Cd core and a ZnO-CdS heterostructural shell	December 2012	570	[157]
ZnO/TiO2	Composite nanofibers	February 2010	386.5	[168]	Superior PC activity of ZnO/TiO2 composite nanofibers. The reason behind that was superior light harvesting capacity and better quantum efficiency.
ZnO/TiO2	Nanoscale coupled oxides	June 2010	460	[176]	Better UV-Vis absorption for ZnO/TiO2 approximately band edge at 460 nm. Enhanced photocatalytic activity for coupled ZnO/TiO2 due to bonded heterostructures, thus increasing quantum efficiency.
ZnO-SnO2	Nanoporous ZnO-SnO2 heterojunction	June 2012	390	[182]	Nanoporous heterojunction of ZnO-SnO2 exhibited excellent photocatalytic behavior although UV-Vis band edge was not higher than ZnO.
ZnO/SnO2	Nanofibers	May 2010	396	[189]	Mesoporous ZnO/SnO2 nanofibers were synthesized with Sn % content from 25, 33, and 50% and then calcinated at different temperatures. UV-Vis absorption spectroscopy was done and band edges were at about 390 nm. Photodegradation was better for the sample with molar ratio of Zn : Sn 2 : 1 and calcinated at 500°C.
ZnO-SnO2	Hollow spheres and hierarchical nanosheets	November 2007	390	[190]	Higher photocatalytic efficiency due to increased life time of photogenerated electron-hole pair and also the nanosheets provided the favorable condition for the transfer of electron-hole to the surface.
Mn-ZnO/graphene	NPs	April 2014	600	[205]	Enhanced photocatalysis was observed for 3% Mn-ZnO/graphene nanocomposite and UV-Vis DRS showed better results for Mn-ZnO/graphene.
(GO/ZnO)	GO/ZnO nanorods hybrid	November 2014	600	[206]	The synergic effect between GO and ZnO was responsible for an improved photogenerated carrier separation. 3% GO/ZnO showed superior photocatalytic activity.
ZnO/Ag2S	Core-shell nanorods	August 2014	700	[216]	The absorption peak also shifted to 470 nm from 374 nm, while overall absorbance spectrum was broadened up to 700 nm. The photodegradation results were also much better than ZnO nanorods.
ZnO/Ag2S	CSNPs	August 2015	550	[217]	Visible region exhibits the main peak around 550 nm. A huge difference in efficiency of photocatalytic degradation was observed and ZnO/Ag2S CSNPs showed tremendous results.
ZnO/Ag2S	NPs	June 2012	500	[218]	Photodegradation experiment was carried out under sunlight with nearly constant flux. NPs of ZnO/Ag2S showed better performance than bare ZnO NPs, commercial ZnO, P25, and TiO2 Merck.