Abstract
This article provides an overview of current research into the development, synthesis, photocatalytic bacterial activity, biocompatibility and cytotoxic properties of various visible-light active titanium dioxide (TiO2) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO2 NPs are doped with metal and non-metal elements, modified with carbonaceous nanomaterials, and coupled with other metal oxide semiconductors. Transition metals introduce a localized d-electron state just below the conduction band of TiO2 NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO2 NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO2 NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO2 NPs with carbon nanotubes and graphene sheets also achieve the efficient creation of ROS under visible light irradiation. Furthermore, titanium-based alloy implants in orthopedics with enhanced antibacterial activity and biocompatibility can be achieved by forming a surface layer of Ag-doped titania nanotubes. By incorporating TiO2 NPs and Cu-doped TiO2 NPs into chitosan or the textile matrix, the resulting polymer nanocomposites exhibit excellent antimicrobial properties that can have applications as fruit/food wrapping films, self-cleaning fabrics, medical scaffolds and wound dressings. Considering the possible use of visible-light active TiO2 nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.
Highlights
The overuse of antimicrobials in humans, animal husbandry and aquafarming gives rise to the development of dangerous, antibiotic-resistant bacteria [1,2]
Accordinghlya,vtehbeeeennemragdye obfyrreecsoeamrcbhienrsatoiodnesisigdn iasnsdipsaytnetdheisniztehveisfioblremligohft-laicgthivteoTriOh2epaht.otTohcaetraelyfsotrse. , it deems necessaryTthoeesenihnaclnucdee mtheetapl ahnodtoncoan-tmaleytatlicdoapcitnivg,itcyouopflinTgiOw2ithNsPems bicyonrdeudctuocrsi,nagndbomtohdtifhiceatbioannwdigthap and the recombinagtrioapnhoenfeeolexcidtreoonr –cahrobloenpnaanirostuubned[8e4r–v10i4s]i.bTleheliignhcotriprorraadtioiantioofnth.oMseadnoypaantttseimntopttistahnaiavaeffbeectesn made by its electronic band structure greatly, thereby promoting visible light absorption and a red shift in the researcherbsatnodgdaeps.ign and synthesize visible light-active TiO2 photocatalysts
The valence band (VB) of titania is composed of hybridized states of O-2p and Ti-3d orbitals, while the conduction band (CB) consists of primarily Ti-3d orbitals
Summary
The overuse of antimicrobials in humans, animal husbandry and aquafarming gives rise to the development of dangerous, antibiotic-resistant bacteria [1,2]. By irradiating photocatalytic semiconductors with a photon of sufficient energy (≥band gap energy), an electron in the valence band (VB) is excited to the conduction band (CB), leaving a positive hole in the VB These charge carriers migrate to the photocatalyst surface and can generate highly reactive oxygen species (ROS) such as hydroxyl (OH) and superoxide anion (O2−) radicals, and hydrogen peroxide (H2O2) through the oxidative or reductive path with surface-adsorbed water and oxygen (Figure 1). Apart from bactericidal activity, TiO2 NPs find attractive application in biomedical fields as pNhaonotmodatyerniaalsm20i2c0,th10e,r1a2p4 eutic agents for destroying human cancer cells from the skin to the inte3ronfa5l6 organs under ultraviolet (UV) and visible light illumination [36]. Xu et al inwdithicaatlaerdgetrhsautrfaacneaatraesaeanTdiOsm aNllePrssiezexhthiabnitthaeihr ibguhlkecropunhtoertpoatrotsxigceinteyraatenmdocryetRoOtoSxdiucriitnygin human keratinocyptheotcoeelxlcsittahtiaonn [r8u0]t.ilXeuTeitOal2. iNndPicsa[te8d1]t.haRt eanceatnastelyT, iBOa2 rNtlPest eexthiabli.t ainhdigihceartepdhotthotaotxiocintye-adnidmensional titania nancoyttoutobxeicsitpyrienphaurmedanbkyerealtiencotcryotechceelmls itchaanl aruntoilediTziOat2iNonPse[x81h]i.bRietcseuntplye,rBhayrtdlertoept halo. binidcicbaetehdavior with a large watshtueaptrerchooynnder-tdoapicmhtoeanbnsicigobnleeahlaovftiiot>ran1wi5ait0h◦na.alanSrougteucwbheassteurppcroeenprthaarycetddanrogblpyehofoe l>be1ci5ctr0o°tc.ithSauenmchiiacsaunlpaearnnhoyotdduirzobapethisoonbriecdetxiuthacinbeiiadt bacterial adhesion onnantohtuebiressruerdfuacceedsb[a8ct2e]r.ial adhesion on their surfaces [82]
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