Charge Carrier Processes and Optical Properties in TiO2 and TiO2-Based Heterojunction Photocatalysts: A Review

We describe the main characteristics and advantages of TiO2 as photocatalyst, followed by a summary of historical facts about its application

Stefano Lettieri; Michele Pavone; Ambra Fioravanti; Luigi Santamaria Amato; Pasqualino Maddalena

2021

Scholarcy highlights

  • Why TiO2?In the last three decades, titanium dioxide has been a major subject of study in materials science and technology for its functional properties and its versatility toward different applications
  • We pinpoint the TiO2 limitations and possible ways to overcome them by discussing some of the “hottest” research trends toward solar hydrogen production, which are classified in two categories: approaches based on the use of engineered TiO2 without any cocatalysts
  • No bandgap shift for anatase nanoparticles of diameters down to 2 nm was evidenced by Serpone and coworkers, who suggested that absorption edge blueshifts observed for anatase nanoparticles below 2 nm diameter shall be assigned to a transition from an indirect to direct bandgap excitation, an effect caused by geometric distortions of Ti coordination occurring when anatase particles became ultra-small
  • As a conclusion of this work, we intend to underline the importance of reviewing the basic knowledge on fundamental processes that characterize a functional photocatalyst, even if it is probable that future applications will employ it in significantly modified versions, such as highly reduced forms or as partner material in composite systems and photocatalysts
  • As a consequence we believe that a review might be useful for scholars if it aims at summarizing specific and basic topics, as we did here for the photogenerated charge carrier processes in TiO2
  • Reference reported changes in PL intensity in hierarchical anatase-phase titania with responsivities up to about 1100% at 20% O2 concentrations, which outperformed those obtainable by commercial TiO2 nanopowders up to a factor of about 7 for response to synthetic air
  • The fate and the time dynamics of photogenerated electrons and holes define in a major way the applicative potential of a photocatalyst
  • FCroompyErilgsehvti1e9r.9C4 oEplsyervigiehrtS1c9ie9n4cEelsBe.Vvi.er Science B.V. Monticone and coworkers examined the optical properties of small anatase nanoparticles ofOdMbisffoeenrrvteianctotionpneaarotnifdclqecouswaiznoetrukdmeirs-stsriiofafnels,cotosebxs(aqemruvaiinnnetgudmltihttelceoopnotfriicnnaeolmpberlonupte)esrhitnieftsthfooefrsmabaslol rapntaiotanse particles wisthpnedacintaromapeoatfretriucslltfersao-mosfm3danilflmfeTrdieOon2wt npnaatnrotoi1pclanermtsiicz(lseeesediiFssitgcrouibnruetrt1ioo0vn)e.,rTsohibaesl.edrWavtiaonrdgkisdlithntaloevteofirtbtneheoenbpluuebslhisihftedfor effective marsesppaorprttpiicnrlogexsibwmoitaththiotdnhieaamnodecctdeurirdsrefnrnoctmesurtadntohdwe ntohctecoua1rbrnesenmncce(esoefoeqfFuqiagunuatrnuetmu1m0s)i.zceTohenfeffiendceatmtaednitdenffoetctfit in TiO2 nane.cst.FiovMreomerxeaaosmvseparl,petp,hraeoxbsialmumeaesthioaifnutstahniondrstdhoiedbsanebrovstoesrdupptciphoaonnrttghtehrseesinhooctclhdueroroefsncacinellaaottafosrqeuTaniOtu2massiaze strengths offouepnftcfietcicaotlnitnroaTfnidOsiet2cionrenaasnsoiinnpgtahrpteiac3rl.et5is–c.4lMe.5soesrViezoervsaenbrg,eeltohwweist2ahmndmeecarwuetaahssoinrrsegpopobarsrteteridcvleebd,ywcShhaaitcnohghethsaneinydtchoewooscriklleartsor did not attrie,ntowgtqhhuosaosntftauotepmdtisctiahzlaettreatfhnfeesciteisxobpnuesrtiintmotehinect3ar.le5ar–se4es.du5 leltaVsttmricaaentgcsthereawdinitthihnediterhcecreapalcasurintliagctlipeosan.rsticblaes,ewdhoicnhtthheey efdfeicdtinvoet amttraisbsutaeptoprqouxaimntautmions.izeOenffecatnsobthuet rto hinacnrdea, sendo labttaincedsgtarpainsihniftthefoprartaicnlaetsa.se nanoparticles of diameters down to 2 nm was evidenced by Serpone and coworkers , who suggested that absorption edge blueshifts observed for anatase nanoparticles below 2 nm diameter shall be assigned to a transition from an indirect to direct bandgap excitation, an effect caused by geometric distortions of Ti coordination occurring when anatase particles became ultra-small

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