Holes In Valence Band Research Articles

Charge accumulation kinetics in multi-redox molecular catalysts immobilised on TiO2.

Multi-redox catalysis requires the accumulation of more than one charge carrier and is crucial for solar energy conversion into fuels and valuable chemicals. In photo(electro)chemical systems, however, the necessary accumulation of multiple, long-lived charges is challenged by recombination with their counterparts. Herein, we investigate charge accumulation in two model multi-redox molecular catalysts for proton and CO2 reduction attached onto mesoporous TiO2 electrodes. Transient absorption spectroscopy and spectroelectrochemical techniques have been employed to study the kinetics of photoinduced electron transfer from the TiO2 to the molecular catalysts in acetonitrile, with triethanolamine as the hole scavenger. At high light intensities, we detect charge accumulation in the millisecond timescale in the form of multi-reduced species. The redox potentials of the catalysts and the capacity of TiO2 to accumulate electrons play an essential role in the charge accumulation process at the molecular catalyst. Recombination of reduced species with valence band holes in TiO2 is observed to be faster than microseconds, while electron transfer from multi-reduced species to the conduction band or the electrolyte occurs in the millisecond timescale. Finally, under light irradiation, we show how charge accumulation on the catalyst is regulated as a function of the applied bias and the excitation light intensity.

High-Performance Room-Light-Driven β-AgVO3/mpg-C3N4 Core/Shell Photocatalyst Prepared by Mechanochemical Method

A new highly efficient, visible light active, silver vanadate/polymeric carbonitride “core/shell” photocatalyst was prepared mechano-chemically prepared by grinding mixtures of β-silver vanadate and mesoporous graphitic carbonitride. Besides the core/shell photocatalyst, β-silver vanadate/mesoporous polymeric carbonitride composites and supported mpg-C3N4@β-silver vanadates were prepared. The materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen ad- and de-sorption, diffuse reflectance UV-Vis measurement (DRS), infrared spectroscopy, Raman microscopy, and time-resolved photoluminescence spectroscopy. The photocatalytic performance of the materials was investigated in the degradation of organics using pharmaceutical ibuprofen and 4-(isobutyl phenyl) propionic acid sodium salt as model compounds under batch conditions. Reaction intermediates were studied by electrospray ionization and time-of-flight mass spectrometry (ESI-TOF-MS). Additionally, the degree of mineralization was determined by total organic carbon TOC measurements. The core/shell photocatalyst has shown superior photocatalytic activity compared to the other prepared composites or supported photocatalysts as well as the single mpg-C3N4. Scavenger experiments showed that valence band holes and anionic superoxide radicals are the main active species in the photocatalytic process. TOC measurement confirmed the mineralization of the organic compound, which was in line with ESI-TOF-MS experiments. Time-resolved photoluminescence measurements indicated that charges generated in carbonitride migrate via diffusive hopping and exhibit increased mobility in the case of the silver vanadate/polymeric carbonitride composite.

Role of Intrinsic Surface States in Efficiency Attenuation of GaN‐Based Micro‐Light‐Emitting‐Diodes

The effects of an intrinsic nonpolar surface on internal quantum efficiency (IQE) are numerically investigated for gallium nitride (GaN)‐based micro‐light emitting‐diodes (μ‐LEDs). It is found that due to the modulation of the surface density of states, the surface energy band bends upward, and valence band holes are naturally pushed toward the surface and are accumulated at the surface, resulting in significant nonradiative recombination. Consequently, the intrinsic surface states remarkably affect the IQE of μ‐LEDs with a size of less than 30 μm due to the large surface‐to‐volume ratio, whereas the IQE of devices with a size of more than 30 μm is relatively insensitive to the intrinsic surface states. IQE starts to decrease for devices with a size of 30 μm, even without considering sidewall damage. In particular, starting from a size of 10 μm, μ‐LEDs suffer a significant efficiency loss and the peak current density shifts to a higher value. The results open the way to improving device performance of μ‐LEDs down to 1 μm and beyond, by incorporating surface band engineering combined with surface passivation over the full range of microdisplay applications.

How silicon and boron dopants govern the cryogenic scintillation properties of N-type GaAs

This paper is the first report describing how the concentrations of silicon and boron govern the cryogenic scintillation properties of n-type GaAs. It shows that valence band holes are promptly trapped on radiative centers and then combine radiatively with silicon donor band electrons at rates that increase with the density of free carriers. It also presents the range of silicon and boron concentrations needed for efficient light emission under X-ray excitation, which along with its low band gap and apparent absence of afterglow, make scintillating GaAs suitable for the detection of rare, low-energy electronic excitations from interacting dark matter particles. A total of 29 samples from four different suppliers were studied. Luminosities and timing responses were measured for the four principal emission bands centered at 860, 930, 1070, and 1335 nm, and for the total emissions. Excitation pulses of 40 kVp X-rays were provided by a light-excited X-ray tube driven by an ultra-fast laser. Scintillation emissions from 800 to 1350 nm were measured using an InGaAs photomultiplier. Within the concentration ranges of free carriers from 2 x 1016/cm3 to 6 x 1017/cm3 and boron from 1.5 × 1018/cm3 to 6 x 1018/cm3, nine samples have luminosities > 70 photons/keV and two have luminosities > 110 photons/keV. Other samples in that range have lower luminosities due to higher concentrations of non-radiative centers. The decay times decrease by typically a factor of ten with increasing free carrier concentrations from 1017/cm3 to 2 x 1018/cm3.

DMRG study of exciton condensation in the extended Falicov-Kimball model

The formation and condensation of excitonic bound states of conduction-band electrons and valence-band holes surely belongs to one of the most exciting ideas of contemporary solid state physics. In this short review we present the latest progress in this field reached by the density-matrix-renormalization-group (DMRG) calculations within various extensions of the Falicov-Kimball model. Particular attention is paid to a description of crucial mechanisms (interactions) that affect the stability of the excitonic phase, and namely: (i) the interband $d$-$f$ Coulomb interaction, (ii) the $f$-electron hopping, (iii) the nonlocal hybridization with odd and even parity, (iv) combined effects of the local and nonlocal hybridization, (v) the nearest-neighbor Coulomb interaction between $d$ and $f$ electrons and (vi) the correlated hopping. The relevance of numerical results obtained within different extensions of the Falicov-Kimball model for a description of the real $d$-$f$ materials is widely discussed.

Ferromagnetism of Chalcopyrite AlGaAs2:Mn Quaternary Alloys

The electronic structure and magnetic properties of chalcopyrite (CH) AlGaAs2 with dopant Mn at 3.125 and 6.25 % concentrations are investigated using first-principles calculations. The CH AlGaAs2 alloy is a p-type semiconductor with a small band-gap. The AlGaAs2:Mn shows that the ferromagnetic (FM) state is the most energetically favorable one. The Mn-doped AlGaAs2 exhibits FM and strong half-metallic ground states.The spin polarized Al(Ga,Mn)As2 state (Al-rich system) is more stable than the (Al,Mn)GaAs2 state (Ga-rich system), which has a magnetic moment of 3.82mB/Mn. The interaction between Mn-3d and As-4p states at the Fermi level dominates the other states.The states at the Fermi level are mainlyAs-4p electrons, which mediate strong interaction between the Mn-3d and As-4p states. It is noticeable that the FM ordering of dopant Mn with high magnetic moment originates from the As(4p)-Mn(3d)-As(4p) hybridization, which is attributed to the partially unfilled As-4pbands. The high FM moment of Mn is due to the double-exchange mechanism mediated by valence-band holes.

Excited states in hydrogenated single-layer MoS2

Our calculations of the excitation spectrum of single-layer MoS2 at several hydrogen coverages, using a density-matrix based time-dependent density-functional theory (TDDFT) show that the fully hydrogenated system is metallic, while at lower coverages the spectrum consists of spin-polarized partially filled localized mid-gap states. The calculated absorption spectrum of the system reveals standard excitonic peaks corresponding to the bound valence-band hole and conduction-band electron, as well as excitonic peaks that involve the mid-gap states. Binding energies of the excitons of the hydrogenated system are found to be relatively large (few tens of meV), making their experimental detection facile and suggesting hydrogenation as a knob for tuning the optical properties of single-layer MoS2. Importantly, we find hydrogenation to suppress visible light photoluminescence, in agreement with experimental observations. In contrast, both Li and Na atoms transform the system into an n-doped non-magnetic semiconductor that does not allow excitonic states.

(Invited) Novel Approach of Efficient-Photocatalyst Design Based on Electron Trap-Distribution Analysis

How can we design solid photocatalysts? What is the decisive factor controlling photocatalytic activities?So-called band-structure model (BSM), electrons in a valence band (VB) of a photocatalyst is photoexcited into a conduction band (CB), leaving positive holes in VB, and electrons and holes reduce and oxidize, respectively, substrates adsorbed on the surface of the photocatalyst, does suggest preferable band positions for redox reaction uniquely decided only by crystalline structure. The other possible factors, e.g., particle size and surface structure, cannot be discussed within BSM.Recently, we have developed reversed double-beam photoacoustic spectroscopy (RDB-PAS) which enables measure energy-resolved density of electron traps (ERDT). Those electron traps (ETs) seem to be predominantly located on the surface of almost all the metal oxide particles and therefore they reflect macroscopic surface structure in ERDT patterns [1,2]. Using ERDT pattern along with the data of CB-bottom position (CBB), i.e., ERDT/CBB patterns, it has been shown that metal oxide powders and the other semiconducting materials such as carbon nitrides can be identified without using the other analytical data such as X-ray diffraction patterns or specific surface area, and similarity/differentness of a pair of metal-oxide samples can be quantitatively evaluated as a parameter, ζ, degree of coincidence of ERDT/CBB patterns [3].Three representative photocatalytic reactions, (a) hydrogen (H2) evolution from deaerated aqueous methanol (H2 system), (b) carbon-dioxide (CO2) evolution from aqueous acetic acid under aerobic conditions (CO2 system) and (c) oxygen (O2) evolution from aqueous silver fluoride (O2 system), were carried out with those titania samples, and the ratios of evaluated photocatalytic activities for pairs of titania samples (0 < ζ pc < 1) were compared with ζ. It was observed that the higher the value of ζ at > 0.6 is, the higher becomes ζ pc , i.e., the ERDT/CBB patterns reflect bulk/surface structures which govern overall photocatalytic activities of titania samples; ERDT/CBB patterns can identify these titania samples and this can be extended to the other metal oxides and semiconducting materials such as carbon nitride (C3N4).Then, reversed analysis has been made, i.e., those ERDT/CBB patterns were arranged in the order of photocatalytic activity from higher side to lower side. Interestingly, for CO2 and O2 systems, highest activity titania samples exhibited similar patterns in each system, while middle or low-activity samples did no similarity. One of the possible reasons is that photocatalytic activities are governed by many independent factors, which are all optimized in the highest activity samples, though activities can be much reduced only by one unfavorable factor. In the other words, we cannot expect to find titania samples of activity higher than those titania samples in CO2 and O2 systems. This assumption, however, may suggest that titania samples exhibiting superior photocatalytic activity in H2 system may be discovered, because they seem not to be optimized.[1] Nitta, A.; Takase, M.; Takashima, M.; Murakami, N.; Ohtani, B. Chem. Commun. 2016, 52, 12096-12099.[2] Nitta, A.; Takashima, M.; Murakami, N.; Takase, M.; Ohtani, B. Electrochim. Acta 2018, 264, 83-90.[3] Nitta, A.; Takashima, M.; Takase, M.; Ohtani, B. Catal. Today 2019, 321-322, 2-8.

Synergistic effects between the S-TiO2 photocatalyst and the Fenton-like reagent: Enhanced contaminant oxidation under visible light illumination

Sulfur-doped TiO2 (S-TiO2) coupled with the Fenton-like reagent (i.e., Fe(III) and H2O2) exhibited photochemical activity under visible-light illumination, resulting in the degradation of over 95 % benzoic acid, 95 % carbamazepine, and 99 % 4-chlorophenol within 30 min. The combined system removed contaminants much faster than its uncombined S-TiO2/visible light and Fe(III)/H2O2 counterparts. The synergistic effect between S-TiO2 and the Fenton-like reagent was found to be due to 1) the generation of conduction band electrons and valence band holes in S-TiO2 under visible light illumination; 2) the reduction of Fe(III) by the conduction band electrons, thereby enhancing Fe(II) generation while minimizing electron-hole recombination; 3) the production of •OH from the reactions between Fe(II) and H2O2, and between H2O2 and conduction band electrons; and 4) the oxidation of contaminants by both valence band holes and •OH. Under the experimental conditions employed in this study, the S-TiO2/visible light/Fe(III)/H2O2 system exhibited a sustainable reactivity over 7 testing cycles, with more than 90 % of BA degraded in each cycle.

Strong Valence Band Convergence to Enhance Thermoelectric Performance in PbSe with Two Chemically Independent Controls.

We present an effective approach to favorably modify the electronic structure of PbSe using Ag doping coupled with SrSe or BaSe alloying. The Ag 4d states make a contribution to in the top of the heavy hole valence band and raise its energy. The Sr and Ba atoms diminish the contribution of Pb 6s2 states and decrease the energy of the light hole valence band. This electronic structure modification increases the density-of-states effective mass, and strongly enhances the thermoelectric performance. Moreover, the Ag-rich nanoscale precipitates, discordant Ag atoms, and Pb/Sr, Pb/Ba point defects in the PbSe matrix work together to reduce the lattice thermal conductivity, resulting a record high average ZTavg of around 0.86 over 400-923 K.

Strong Valence Band Convergence to Enhance Thermoelectric Performance in PbSe with Two Chemically Independent Controls

AbstractWe present an effective approach to favorably modify the electronic structure of PbSe using Ag doping coupled with SrSe or BaSe alloying. The Ag 4d states make a contribution to in the top of the heavy hole valence band and raise its energy. The Sr and Ba atoms diminish the contribution of Pb 6s2 states and decrease the energy of the light hole valence band. This electronic structure modification increases the density‐of‐states effective mass, and strongly enhances the thermoelectric performance. Moreover, the Ag‐rich nanoscale precipitates, discordant Ag atoms, and Pb/Sr, Pb/Ba point defects in the PbSe matrix work together to reduce the lattice thermal conductivity, resulting a record high average ZTavg of around 0.86 over 400–923 K.

Performance of EDTA modified magnetic ZnFe2O4 during photocatalytic reduction of Cr(VI) in aqueous solution under UV irradiation

The photocatalytic reduction of toxic Cr(VI) to non-pernicious Cr(III) using ZnFe2O4/EDTA (ethylenediaminetetraacetic acid) under UV irradiation was evaluated. The reduction of Cr(VI) with bare ZnFe2O4 under UV irradiation was negligible. However, the Cr(VI) in the solution was completely reduced within 3 h after the introduction of EDTA. EDTA could consume valence band holes and could be oxidized by holes into inorganic products. Therefore, photo-generated electrons could be used to reduce Cr(VI) to Cr(III). The effect of concentration of EDTA, ZnFe2O4 photocatalyst dosages, and initial pH on the photocatalytic reduction of Cr(VI) was investigated. The results revealed that the photocatalytic reduction of Cr(VI) accelerated by increasing EDTA concentration and ZnFe2O4 dosage. The present reduction process confirms the pseudo-first-order kinetic reaction. The quasi reduction rate constant increased from 3.5 x 10−4 min−1 to 2.6 x 10−2 min−1 with the increase in initial EDTA concentration from 0 to 1000 mg L−1. The acidic solution is preferable for the photocatalytic reduction of Cr(VI). The entire reduction of Cr(VI) was carried out within 2 h under the optimum conditions with pH 2, 20 mg ZnFe2O4, and 500 mg L−1 EDTA. The formation of [Cr–EDTA]3+ complex may be advantageous to accelerate the Cr(VI) reduction. A probable mechanism for the photocatalytic Cr(VI) reduction was speculated here.

Construction of novel direct Z-scheme AgIO4-g-C3N4 heterojunction for photocatalytic hydrogen production and photodegradation of fluorescein dye

Highly mesoporous AgIO4/g-C3N4 heterojunctions were synthesized by sonochemical route for exceptional photocatalytic degradation of fluorescein dye (FLU) and hydrogen production. AgIO4 nanoparticles are deposited on the corners and edges of the wrinkled sheets of g-C3N4. Mass ratio of AgIO4 acted a pivotal part in enhancing the photocatalytic reactivity. Due to the small difference between the valence band potential of g-C3N4 (EVB = +1.4 eV) and conduction band potential of AgIO4 (ECB = +1.08 eV), a perfect direct Z-scheme mechanism is constructed. Noticeably, the removal of fluorescein dye reach 98% and the rate of hydrogen produced is 23 mmolh−1 g−1. Taking the benefits of matching the band energy structure, AgIO4/g-C3N4 heterojunction enhances the recombination of the useless positive hole and electron in the inferior valence and conduction band of g-C3N4 and AgIO4, respectively through Z-scheme aspects. However, the holes and electrons in the higher valence and conduction band are preserved with strong oxidation and reduction power. This Z-scheme mechanism not only enhances the quantum efficiency of charge separation, but also, increase the oxidative and reductive power of the charge carrier. Positive holes and the superoxide radicals are the main reactive species confirmed the Z-scheme mechanism. This research work give a hot spot in synthesis of low cost novel photocatalyst for hydrogen production and wastewater treatment.

Efficient conversion of bicarbonate (HCO3−) to acetate and simultaneous heavy metal Cr(VI) removal in photo-assisted microbial electrosynthesis systems combining WO3/MoO3/g-C3N4 heterojunctions and Serratia marcescens electrotroph

The removal of the hazardous heavy metal Cr(VI) in water and the simultaneous production of acetate from the reduction of inorganic carbon (HCO3−) is demonstrated in a photo-assisted microbial electrosynthesis (MES) system incorporating WO3/MoO3/g-C3N4 Z-scheme heterojunctions and Serratia marcescens Q1 electrotroph cathode. The rates of acetate production (6.1 ± 0.3 mg/L/h) and Cr(VI) removal (4.5 ± 0.1 mg/L/h) recorded at a circuital current of 2.8 ± 0.1 A/m2 were 2.4-fold (acetate production), 1.7-time (Cr(VI) removal) and 1.6-fold (circuital current) of those in the controls recorded in the absence of WO3/MoO3/g-C3N4, and 1.6-fold (acetate production) and 1.8-time (circuital current) of those in the absence of both Cr(VI) and WO3/MoO3/g-C3N4. Photogenerated WO3/MoO3/g-C3N4 conduction bands electrons favored both direct or indirect (via S. marcescens) reductions of Cr(VI) and H+, with the latter producing H2 which was further metabolized by S. marcescens with HCO3− to yield acetate. The higher circuital current drawn under photoirradiation conditions refilled the photo-generated valence band holes in the semiconductor and provided the driving force for the reduction reactions. This study provides an alternative and feasible approach for achieving complete removal of toxic heavy metal from water and industrial waters with simultaneous conversion of inorganic carbon to key block chemicals.

Insights into Interface Charge Extraction in a Noble-Metal-Free Doped Z-Scheme NiO@BiOCl Heterojunction

It is of great significance to thoroughly explore the interface charge extraction and migration in heterojunction systems, which could guide us to synthesize higher-efficiency photocatalytic materials. A novel noble-metal-free doped Z-scheme NiO@BiOCl heterojunction was found in this work. The corresponding heterostructure, interface electron extraction, and electron migration were investigated via first-principles calculation. 5,5′-dimethyl-1-pyrroline-N-oxide (DMPO) spin-trapping electron spin resonance (ESR) and time-resolved photoluminescence (TRPL) tests were implemented to confirm the calculation results, which showed that electrons and holes stayed in the NiO (100) facet and BiOCl (110) facet, respectively. Owing to the large chemical potential of 2.40 V (vs ENHE) for the BiOCl valence-band hole, it possessed super activity to oxidize water into hydroxyl radicals or molecular oxygen. We hope this promising multifunctional photocatalytic material, therefore, NiO@BiOCl can be applied in advanced treatment of organic wastewater and oxygen production from photolysis water.

2D/2D/3D architecture Z‑scheme system for simultaneous H2 generation and antibiotic degradation

The construction of p-n heterojunction is a workable approach for the expansion of light absorption range and the suppression of charge-carrier recombination to enhance the photocatalytic performance. However, the redox ability of dominant band potential in each semiconductor is restrained by heterostructure. In this work, the reduced graphene oxide (RGO) was used as an adhesive to integrate Cu2O and BiVO4 via a two-step solvothermal method, fabricating a Z-scheme photocatalytic system. The 2D/2D/3D Cu2O/RGO/BiVO4 system exhibited excellent photocatalytic performance on simultaneous tetracycline degradation (TC) and H2 production due to the high redox ability. The highest H2 production achieved by the 7/G40/3 sample was about 6 times higher than that of Cu2O with the TC degradation rate of 20.3%. In the whole degradation, the 7/G40/3 sample also exhibited the optimal degradation efficiency for TC of 96% after 3 h under visible light irradiation. And various experimental and test results demonstrated that RGO played a significant role in the combination of the conduction band electrons of BiVO4 and the valence band holes of Cu2O, enriching electrons and holes in the dominant energy band, respectively. This study highlights the rational integration of H2 production and pollutant degradation by taking full advantage of the Z-scheme photocatalytic system.

Remarkable Improvement of Thermoelectric Figure-of-Merit in SnTe through In Situ-Created Te Nanoinclusions

SnTe exhibits very low Seebeck coefficient along with high electrical–thermal conductivities owing to very high hole concentration that results from intrinsic Sn vacancies. All these unfavorable thermoelectric parameters restrict pristine SnTe from becoming an outstanding thermoelectric material. In this work, we demonstrate the improvement in figure-of-merit of SnTe through in situ creation of Te nanoinclusions in the SnTe matrix. We have intentionally added excess Te in stoichiometric Sn/Te (1:1) for the synthesis of SnTe. During solidification of SnTe from the melt, the excess Te in the liquid state gets expelled to the grain boundaries. On further cooling, when Te starts to solidify, it exerts strain in the already solidified SnTe grains and creates extensive structural defects including dislocations, twin boundaries, and subgrain boundaries that scatter phonons of midwavelength. The point defect due to intrinsic Sn vacancies and SnTe/Te grain boundaries respectively scatters phonons of low and high wavelengths. Effective scattering of the entire spectrum of phonons through the hierarchical defects gives rise to an ultralow lattice thermal conductivity of 0.5 W m–1 K–1 that is close to the theoretical minimum limit. The contribution from the heavy hole valence band in transport along with energy filtering of charge carriers at the SnTe/Te interface results in improvement of the Seebeck coefficient near room temperature. The cumulative effect of improved Seebeck coefficient and suppressed thermal conductivity gives rise to a high figure-of-merit (ZT) value of ∼1.5 at 750 K and an average ZT of ∼0.48 for the Sn0.9Te sample.

Antimony-Doped Tin Oxide Nanocrystals for Enhanced Photothermal Theragnosis Therapy of Cancers.

The doped semiconductor nanocrystal with free holes in valence band exhibits strong near-infrared (NIR) local surface plasmon resonance effects, which is essential for photothermal agents. Herein, the hydrophilic Sb doped SnO2 nanocrystals were successfully prepared by a simple hydrothermal synthesis method. The doping makes the Sb doped SnO2 nanocrystals possessing defect structures. Compared with the un-doped SnO2 nanocrystals, Sb doped SnO2 nanocrystals exhibit stronger absorption in the NIR region from 500 to 1,100 nm and higher photothermal conversion efficiency (up to 73.6%) which makes the synthesized Sb doped SnO2 nanocrystals be used as excellent photothermal agents. Importantly, Sb doped SnO2 nanocrystals can efficiently kill cancer cells both in vitro and in vivo under the irradiation of a 980 nm laser with a power density of 0.6 W cm–2. In addition, Sb doped SnO2 nanocrystals can also be served as efficient CT imaging agents owing to the large X-ray attenuation coefficient of tin.

Emergence of pure spin current in doped excitonic magnets

An excitonic magnet hosts a condensate of spin-triplet excitons composed of conduction-band electrons and valence-band holes, and may be described by the two-orbital Hubbard model. When the Hamiltonian has the nearest-neighbor interorbital hopping integrals with $d$-wave symmetry and the number of electrons is slightly away from half filling, the $\boldsymbol{k}$-space spin texture appears in the excitonic phase with a broken time-reversal symmetry. We then show that, applying electric field to this doped excitonic magnet along a particular direction, a pure spin current emerges along its orthogonal direction. We discuss possible experimental realization of this type of the pure spin current in actual materials.

(Invited) Novel Approach of Efficient-Photocatalyst Design Based on Electron Trap-Distribution Analysis

How can we design solid photocatalysts? What is the decisive factor controlling photocatalytic activities? So-called band-structure model (BSM), electrons in a valence band (VB) of a photocatalyst is photoexcited into a conduction band (CB), leaving positive holes in VB, and electrons and holes reduce and oxidize, respectively, substrates adsorbed on the surface of the photocatalyst, does suggest preferable band positions for redox reaction uniquely decided only by crystalline structure. The other possible factors, e.g., particle size and surface structure, cannot be discussed within BSM.Recently, we have developed reversed double-beam photoacoustic spectroscopy (RDB-PAS) which enables measure energy-resolved density of electron traps (ERDT). Those electron traps (ETs) seem to be predominantly located on the surface of almost all the metal oxide particles and therefore they reflect macroscopic surface structure in ERDT patterns [1,2]. Using ERDT pattern along with the data of CB-bottom position (CBB), i.e., ERDT/CBB patterns, it has been shown that metal oxide powders and the other semiconducting materials such as carbon nitrides can be identified without using the other analytical data such as X-ray diffraction patterns or specific surface area, and similarity/differentness of a pair of metal-oxide samples can be quantitatively evaluated as a parameter, ζ, degree of coincidence of ERDT/CBB patterns [3].Three representative photocatalytic reactions, (a) hydrogen (H2) evolution from deaerated aqueous methanol (H2 system), (b) carbon-dioxide (CO2) evolution from aqueous acetic acid under aerobic conditions (CO2 system) and (c) oxygen (O2) evolution from aqueous silver fluoride (O2 system), were carried out with those titania samples, and the ratios of evaluated photocatalytic activities for pairs of titania samples (0 < ζ pc < 1) were compared with ζ. It was observed that the higher the value of ζ at > 0.6 is, the higher becomes ζ pc , i.e., the ERDT/CBB patterns reflect bulk/surface structures which govern overall photocatalytic activities of titania samples; ERDT/CBB patterns can identify these titania samples and this can be extended to the other metal oxides and semiconducting materials such as carbon nitride (C3N4).Then, reversed analysis has been made, i.e., those ERDT/CBB patterns were arranged in the order of photocatalytic activity from higher side to lower side. Interestingly, for CO2 and O2 systems, highest activity titania samples exhibited similar patterns in each system, while middle or low-activity samples did no similarity. One of the possible reasons is that photocatalytic activities are governed by many independent factors, which are all optimized in the highest activity samples, though activities can be much reduced only by one unfavorable factor. In the other words, we cannot expect to find titania samples of activity higher than those titania samples in CO2 and O2 systems. This assumption, however, may suggest that titania samples exhibiting superior photocatalytic activity in H2 system may be discovered, because they seem not to be optimized.[1] Nitta, A.; Takase, M.; Takashima, M.; Murakami, N.; Ohtani, B. Chem. Commun. 2016, 52, 12096-12099.[2] Nitta, A.; Takashima, M.; Murakami, N.; Takase, M.; Ohtani, B. Electrochim. Acta 2018, 264, 83-90.[3] Nitta, A.; Takashima, M.; Takase, M.; Ohtani, B. Catal. Today 2019, 321-322, 2-8.