A Photocatalytic Hydrolysis and Degradation of Toxic Dyes by Using Plasmonic Metal–Semiconductor Heterostructures: A Review

Abstract

Converting solar energy to chemical energy through a photocatalytic reaction is an efficient technique for obtaining a clean and affordable source of energy. The main problem with solar photocatalysts is the recombination of charge carriers and the large band gap of the photocatalysts. The plasmonic noble metal coupled with a semiconductor can give a unique synergetic effect and has emerged as the leading material for the photocatalytic reaction. The LSPR generation by these kinds of materials has proved to be very efficient in the photocatalytic hydrolysis of the hydrogen-rich compound, photocatalytic water splitting, and photocatalytic degradation of organic dyes. A noble metal coupled with a low bandgap semiconductor result in an ideal photocatalyst. Here, both the noble metal and semiconductor can absorb visible light. They tend to produce an electron–hole pair and prevent the recombination of the generated electron–hole pair, which ultimately reacts with the chemicals in the surrounding area, resulting in an enhanced photocatalytic reaction. The enhanced photocatalytic activity credit could be given to the shared effect of the strong SPR and the effective separation of photogenerated electrons and holes supported by noble metal particles. The study of plasmonic metal nanoparticles onto semiconductors has recently accelerated. It has emerged as a favourable technique to master the constraint of traditional photocatalysts and stimulate photocatalytic activity. This review work focuses on three main objectives: providing a brief explanation of plasmonic dynamics, understanding the synthesis procedure and examining the main features of the plasmonic metal nanostructure that dominate its photocatalytic activity, comparing the reported literature of some plasmonic photocatalysts on the hydrolysis of ammonia borane and dye water treatment, providing a detailed description of the four primary operations of the plasmonic energy transfer, and the study of prospects and future of plasmonic nanostructures.

Catecholate Dye-Assisted Decoration of Ag on TiO2 Nanoparticles for Detection of Cancer-Related MicroRNA Biomarkers on a Multiplexed Photoelectrochemical Platform

“…15,27 Following light absorption, LSPRs are generated in the Ag NPs, which undergo nonradiative electromagnetic decay to produce hot electron−hole pairs. 15,34,52 Plasmonic NPs can generate hot electron−hole pairs at a wide range of frequencies correlating with their extinction spectra, which means the presence of plasmonic Ag NPs within TiO 2 /HTX/Ag NP directly enhances the IPCE of this material system in both UV and visible light. 15,34,52 Even though a molecular layer of HTX separates the TiO 2 /Ag junction, the Ag NPs are still close enough to the TiO 2 NPs to cause Fermi level equilibration and band bending of the TiO 2 conduction and valence bands.…”

“…15,34,52 Plasmonic NPs can generate hot electron−hole pairs at a wide range of frequencies correlating with their extinction spectra, which means the presence of plasmonic Ag NPs within TiO 2 /HTX/Ag NP directly enhances the IPCE of this material system in both UV and visible light. 15,34,52 Even though a molecular layer of HTX separates the TiO 2 /Ag junction, the Ag NPs are still close enough to the TiO 2 NPs to cause Fermi level equilibration and band bending of the TiO 2 conduction and valence bands. 53,54 In this scheme, initial light absorption by Ag NPs results in LSPR generation which decays by direct injection of a hot electron into the LUMO of HTX.…”

“…This is due to the improved photoexcited electron injection into the conduction band and the reduced energy barrier of the semiconductors. ,, The highest occupied molecular orbital level and lowest unoccupied molecular orbital (LUMO) level of HTX are positioned at −5.64 and −0.19 eV, respectively . Likewise, in unmodified P25-TiO 2 , the bandgap is 3.15 eV and the conduction band level is approximately at −4.20 eV. , As the LUMO level of HTX is higher than the conduction band level of TiO 2 , photoexcitation is made more efficient through the type-I photoelectron injection process, where electrons can directly transition from the LUMO of a photoexcited surface-adsorbed molecule to conduction band of a semiconductor. ,, Since dye molecules like HTX can be photoexcited at a wide range of frequencies in both UV and visible light, the type-I photoelectron injection process is able to significantly enhance the photoexcitation efficiency of the TiO 2 /HTX NP heterostructure. ,, When plasmonic Ag NPs are added to this system, it results in the formation of a Schottky barrier between the Ag NP and the HTX-modified TiO 2 , where Fermi level equilibration of TiO 2 and Ag produces band bending in the conduction and valence bands of TiO 2 . ,, When a plasmonic metal nanostructure with a higher work function comes in contact with an n-type semiconductor like TiO 2 , a Schottky barrier is formed. , This results in band bending in the semiconductor and lowers the conduction band energy level closer to the Fermi level of the plasmonic nanostructure, enabling efficient hot electron generation via LSPR decay. , Following light absorption, LSPRs are generated in the Ag NPs, which undergo nonradiative electromagnetic decay to produce hot electron–hole pairs. ,, Plasmonic NPs can generate hot electron–hole pairs at a wide range of frequencies correlating with their extinction spectra, which means the presence of plasmonic Ag NPs within TiO 2 /HTX/Ag NP directly enhances the IPCE of this material system in both UV and visible light. ,, Even though a molecular layer of HTX separates the TiO 2 /Ag junction, the Ag NPs are still close enough to the TiO 2 NPs to cause Fermi level equilibration and band bending of the TiO 2 conduction and valence bands. , In this scheme, initial light absorption by Ag NPs results in LSPR generation which decays by direct injection of a hot electron into the LUMO of HTX. The excited HTX molecule then undergoes type-I photoelectron injection to excite TiO 2 . ,,, The hot holes generated in the Ag NPs are transferred to hole scavengers in the electrolyte solutionsuch as the l -ascorbic acid used in our experimentsto...…”

“…15,27 Following light absorption, LSPRs are generated in the Ag NPs, which undergo nonradiative electromagnetic decay to produce hot electron−hole pairs. 15,34,52 Plasmonic NPs can generate hot electron−hole pairs at a wide range of frequencies correlating with their extinction spectra, which means the presence of plasmonic Ag NPs within TiO 2 /HTX/Ag NP directly enhances the IPCE of this material system in both UV 53,54 In this scheme, initial light absorption by Ag NPs results in LSPR generation which decays by direct injection of a hot electron into the LUMO of HTX. The excited HTX molecule then undergoes type-I photoelectron injection to excite TiO 2 .…”

Photocatalytic Degradation of Some Typical Antibiotics: Recent Advances and Future Outlooks

“…Moreover, pristine Ag 2 O also exhibits poor stability and rapid electron-hole recombination [ 64 ]. Their superior photocatalytic performance on antibiotic degradation depends not only on the reduced electron-hole recombination but may also be from broad and strong absorption ranges in the visible region due to the localized surface plasmon resonance effects induced by Ag nanoparticles [ 3 , 7 , 65 ].…”