Interparticle Charge Transfer Research Articles

Incorporation of Bi sintering aid to TiO2 photoanode for low temperature dye sensitized solar cell

The low conversion efficiency for low temperature dye sensitized solar cells (DSSCs) due to poor interparticle contact and charge transfer of TiO2 photoanode has been an issue for the solar cell. Therefore, the research aims to combat the issue with the implementation of bismuth (Bi) nanoparticles as sintering aid to the TiO2 photoanode. The addition of Bi sintering aid was found to form necks at the TiO2-Bi matrix seen in the morphological studies, despite the low sintering temperature of 200°C, due to the low melting point of Bi (271.4°C). The formation of these necks improved the interparticle contact and charge transfer of the photoanode that was observed in the electron transfer studies. Photoanodes with Bi sintering aid yielded lower charge transfer resistance (RCT) and series resistance (RS) than bare TiO2 photoanode by 15%-31%. The RCT and RS of TiO2-4%Bi photoanode (RCT=7.244 kΩ/cm2, RS=14.64 kΩ/cm2) was even almost comparable to the commercially prepared TiO2 photoanode at high temperature of 450°C (RCT=5.125 kΩ/cm2, RS=10.34 kΩ/cm2). Thus, indicating the potential for this approach in enhancing the overall performance of flexible low temperature DSSC in the future.

Surface-enhanced Raman Scattering and Localized Surface Plasmon Resonance Detection of Aldehydes Using 4-ATP Functionalized Ag Nanorods

Formaldehyde, acetaldehyde, and benzaldehyde are well-known carcinogens affecting human health adversely. Thus, there is a need for efficient detection of these aldehydes. This work uses 4-aminothiophenol (4-ATP) functionalized silver nanorods (Ag NRs) to detect these three aldehydes. The detection mode includes localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS). The LSPR band of 4-ATP functionalized Ag NRs shows a linear decrease in absorbance with the increase in formaldehyde and acetaldehyde concentrations. A sensitivity of 0.96 and 0.79 ΔA/mM for formaldehyde and acetaldehyde were obtained. In the case of benzaldehyde, a nearly exponential decrease in absorbance with the increase in concentrations was observed. Above 98.4 μM concentration, the absorbance diminishes completely. The LoD for formaldehyde and acetaldehyde detection using LSPR is 33.8 and 24.6 μM, respectively. The SERS studies reveal that the 4-ATP binds to Ag NRs through both –SH and –NH2 groups and facilitates the inter-particle charge transfer process. The appearance of b2 modes of vibration for 4-ATP evidences this charge transfer process. In the presence of aldehydes, the change in the band shape, relative intensities, and band position were observed primarily in b2 modes of vibration, evidencing the modulation in the charge transfer process. These remarkable changes were seen in μM concentration of aldehydes. Therefore, detection of these aldehydes with 4-ATP functionalized Ag NRs using SERS is possible in concentrations as low as ~ 1 μM.

Investigating particle-particle electrostatic effects on charged lunar dust transport via discrete element modeling

NASA surface exploration missions have always seen negative effects of dust including the Apollo missions. The astronaut-witnessed unusual behavior of the dust particles that surround the vehicle after engine cutoff has the potential to have more of an influence on surface systems dust loading than the high velocity lunar rocket plume ejecta in the landing process. The levitation and transport of the fine components of regolith on lunar surface has been linked to electrostatic effects and electric field, but so far there is no accurate model considering the inter-particle electrostatic interactions, especially when the particles are charged by rocket plume or other mechanical interactions due to exploration activities. This study is proposed to investigate the dynamics of charged lunar regolith with a discrete element method (DEM) approach focusing on the inter-particle interactions and contact charge transfer. The grain dynamics is coupled with mechanical and electrical particle interactions, and both short- and long-range interactions between spherical particles are incorporated. A tribo-charging model based on instantaneous collisions between particles is adopted and validated by comparing the simulation results to existing experimental data. Sensitivity analysis is conducted to quantify the effects of initial charge, tribo-charging, and E-field on transport of lunar dust based on JSC-1 simulants with a radius of 50 μm. DEM simulations are also conducted in a near realistic lunar environment with the estimations of initial conditions that shows the difference in position and velocity distributions between charged particles and uncharged particles. The results indicate that the charged dust particles have higher dispersion of position and velocity by several orders of magnitude due to electrostatic effects. This provides a potential explanation for the phenomena of the approximately 30 s dust lofting following Apollo Lunar Module landing.

Multiscale modeling of the dynamical conductivity of self-assembled nanoparticle networks: Numerical simulations vs analytical models

Impedance spectroscopy experiments are able to reveal the fundamental charge transport properties of a wide variety of complex disordered and nano-structured materials provided that appropriate modeling tools are used. In this paper, we present a numerical simulation-based approach to model the dynamical conductivity of networks formed by self-assembled metal nanoparticles. Inter-particle nano-resistance and nano-capacitance are implemented at the nano-scale assuming inter-particle charge transfer and accumulation mechanisms that can be adapted depending on the nature of the nano-particles and the surrounding medium. The actual positions and spatial arrangements of the nanoparticles within the network are taken into consideration, allowing the attributes of percolating conducting routes to be extracted, classified, and compared in terms of path conductance and statistical distribution of path lengths. Our findings are contrasted to those obtained using analytic models, which are commonly used, but rely on strong assumptions about the electric properties of the conducting paths. We address these assumptions and show that in the case of weakly disordered systems, there is a general agreement between numerical simulations and analytic modeling-based approaches. In the case of disordered networks where the nano-particle size and position fluctuations are included, we show that the path length distribution is frequency-dependent and can differ significantly from the lognormal distribution usually assumed in the analytic models. The impedance of individual pathways may be extracted from the numerical simulations; we discovered that the conductance and susceptance of a specific path are frequency-dependent and inversely proportional to the path length only in ordered networks. Strong scattering of conductance values is caused by disorder effects. The developed numerical approach is generic and applies to most nano-devices where charge transport relies on percolation; it allows to bridge the gap between the nano-scale and micro-scale electric characteristics and, thus, permits a deeper understanding of the charge transport properties of nano-structured materials.

Unravelling the ultrafast charge dynamics in PbS quantum dots through resonant Auger mapping of the sulfur K-edge

There is a great fundamental interest in charge dynamics of PbS quantum dots, as they are promising for application in photovoltaics and other optoelectronic devices. The ultrafast charge transport is intriguing, offering insight into the mechanism of electron tunneling processes within the material. In this study, we investigated the charge transfer times of PbS quantum dots of different sizes and non-quantized PbS reference materials by comparing the propensity of localized or delocalized decays of sulfur 1s core hole states excited by X-rays. We show that charge transfer times in PbS quantum dots decrease with excitation energy and are similar at high excitation energy for quantum dots and non-quantized PbS. However, at low excitation energies a distinct difference in charge transfer time is observed with the fastest charge transfer in non-quantized PbS and the slowest in the smallest quantum dots. Our observations can be explained by iodide ligands on the quantum dots creating a barrier for charge transfer, which reduces the probability of interparticle transfer at low excitation energies. The probability of intraparticle charge transfer is limited by the density of available states which we describe according to a wave function in a quantum well model. The stronger quantum confinement effect in smaller PbS quantum dots is manifested as longer charge transfer times relative to the larger quantum dots at low excitation energies.

The synergistic effect of anatase and brookite for photocatalytic generation of hydrogen and diclofenac degradation

The development of promising technologies (eco-friendly, cost-effective and simple) for fuel generation and removal of organic pollutants has attracted extensive attention in recent years worldwide. Accordingly, heterogeneous photocatalysis has been considered as most recommended since various chemical reactions could be carried out on the surface of recyclable photocatalysts under sole irradiation (preferably solar). This paper presents the crucial role of the synergistic effect between brookite and anatase titania photocatalysts for their potential application in H2 generation and removal of organic pollutants. Here, a facile hydrothermal treatment of an alkaline solution of Ti2(SO4)3, containing Na+, NH4+, and glycine/Na+ was used to prepare titania photocatalysts in the form of brookite (B), anatase (A), and binary phase (BA), respectively. The comparative photocatalytic activities of obtained photocatalysts and the “standard” P25-TiO2 have been evaluated by the photocatalytic hydrogen evolution (with in situ platinum deposition as a co-catalyst), and photodegradation and mineralization of diclofenac under UV/vis and UV-A, respectively. It has been found that the most active photocatalyst contains 38.2% brookite and 61.8% anatase, has the highest specific surface area (62.3 m2 g-1), and the highest light harvesting ability (absorption edge at 399 nm). The synergistic effect has been confirmed for both tested reactions in comparison to the activities of single-phase photocatalysts. Moreover, the obtained activities are around two times higher than that by famous P25 of similar surface properties. Based on the scavenger tests’ study, the new mechanism for brookite-anatase composites has been proposed, i.e., interparticle charge transfer excitation (ICTE), in which electrons are excited from the valence band (VB) of anatase to the conduction band (CB) of brookite, with simultaneous charge migration according to the heterojunction type II.

Electrospun Highly Crystalline ZnO Nanofibers: Super‐Efficient and Stable Photocatalytic Hydrogen Production Activity

AbstractZnO has tremendous potential in photocatalysis, but only has moderate activity and poor stability because of the sluggish charge transfer and easy aggregation problem, respectively. In this work, ZnO photocatalyst with well‐defined one dimensional (1D) nanofiber structure was successfully fabricated for overcoming these defects. The results revealed that the ZnO nanofibers consist of compactly packed particles that form a cylinder type fiber in highly crystalline and high purity. The robust 1D nanostructure not only can suppress the aggregation of nanoparticles, but also facilitate the interparticle charge transfer. Besides, the mesoporous structure generated through the ZnO particle‐particle interconnection can promote the adsorption of reactants and desorption of products. Benefiting from these merits, the ZnO nanofibers photocatalyst presented superior higher and stable hydrogen production ability than that of nanoparticles counterpart. The photocatalytic hydrogen generation rate of the ZnO nanofibers was estimated to be 1031.8 μmol g−1 h−1, which was about 1.5 times higher than that of ZnO nanoparticles. Moreover, the ZnO nanofibers photocatalyst can maintain its 93.2 % H2‐production rate after five recycle experiments, whereas only 55.8 % for ZnO nanoparticles. This study provides an effective way to solve the energy problem by using solar energy.

Ag Ion Soldering: An Emerging Tool for Sub-nanomeric Plasmon Coupling and Beyond.

Self-assembly represents probably the most flexible way to construct metastructured materials and devices from a wealth of colloidal building blocks with synthetically controllable sizes, shapes, and elemental compositions. In principle, surface capping is unavoidable during the synthesis of nanomaterials with well-defined geometry and stability. The ligand layer also endows inorganic building blocks with molecular recognition ability responsible for their assembly into desired structures. In the case of plasmonic nanounits, precise positioning of them in a nanomolecule or an ordered nanoarray provides a chance to shape their electrodynamic behaviors and thereby assists experimental demonstration of modern nanoplasmonics toward practical uses. Despite previous achievements in bottom-up nanofabrication, a big challenge exists toward strong coupling and facile charge transfer between adjacent nanounits in an assembly. This difficulty has impeded a functional development of plasmonic nanoassemblies. The weakened interparticle coupling originates from the electrostatic and steric barriers of ionic/molecular adsorbates to guarantee a good colloidal stability. Such a dilemma is rooted in fundamental colloidal science, which lacks an effective solution. During the past several years, a chemical tool termed Ag ion soldering (AIS) has been developed to overcome the above situation toward functional colloidal nanotechnology. In particular, a dimeric assembly of plasmonic nanoparticles has been taken as an ideal model to study plasmonic coupling and interparticle charge transfer. This Account starts with a demonstration of the chemical mechanism of AIS, followed by a verification of its workability in various self-assembly systems. A further use of AIS to realize postsynthetic coupling of DNA-directed nanoparticle clusters evidences its compatibility with DNA nanotechnology. Benefiting from the sub-nanometer interparticle gap achieved by AIS, a conductive pathway is established between two nanoparticles in an assembly. Accordingly, light-driven charge transfer between the conductively bridged plasmonic units is realized with highly tunable resonance frequencies. These situations have been demonstrated by thermal/photothermal sintering of silica-isolated nanoparticle dimers as well as gap-specific electroless gold/silver deposition. The regioselective silver deposition is then combined with galvanic replacement to obtain catalytically active nanofoci (plasmonic nanogaps). The resulting structures are useful for real time and on-site Raman spectroscopic tracking of chemical reactions in the plasmonic hotspots (nanogaps) as well as for study of plasmon-mediated/field-enhanced catalysis. The Account is concluded by a deeper insight into the chemical mechanism of AIS and its adaption to conformation-rich structures. Finally, AIS-enabled functional pursuits are suggested for self-assembled materials with strongly coupled and easily reshapable physicochemical properties.

Majority Charge Carrier Transport in Particle-Based Photoelectrodes

The interparticle charge transfer of particle-based photoelectrodes was investigated using a particle-based LaTiO2N photoelectrode as model system. The thickness-dependent front- to back-side illumination photocurrent ratio was measured and compared to the numerical photogenerated current ratio. This comparison suggested the presence of majority charge carrier transport limitations and estimated that only a particle-based film thickness of 450 nm was contributing to the photocurrent. We introduced three different theoretical interparticle charge transfer mechanisms and implemented their respective equations in a computational model. The calculated photocurrent–voltage curves were compared to experimental data and proved that interparticle charge transfer is negligible. Only the particles in direct contact with the fluorine-doped tin oxide glass substrate were contributing to the photocurrent. Thus, more efficient particle-based photoelectrodes should incorporate efficient conductive networks connecting pa...

Hydrogen evolution using CdWO4 modified by BiFeO3 in the presence of potassium iodide; a combination of photocatalytic and non-photocatalytic water splitting

Novel heterogeneous structure of BiFeO3–CdWO4 with different molar ratios was applied for the photocatalytic hydrogen evolution in a self-designed externally UV/visible irradiated photoreactor in the presence of potassium iodide. The photocatalysts were synthesized by simple hydrothermal method and characterized by XRD, FE-SEM-mapping, TEM, UV–Vis DRS, PL, EIS, transient photocurrent and Mott-schottky techniques to identify the structural, optical and photoelectrochemical properties. The slope of Mott-schottky plots confirmed the p-type and n-type conductivity of the synthesized BiFeO3 and CdWO4, respectively. The p-n heterojunctions exhibited more efficiently light absorption, charge separation and electron mobility relative to the pure photocatalysts. We observed that coupling 40 mol% BiFeO3 with CdWO4 provided the best photocatalytic performance of hydrogen evolution, 268.90 μmol h−1.gcat−1 from distilled water and 379.43 μmol h−1.gcat−1 from 0.05 M KI aqueous solution. Iodine species increased H2 evolution efficiency because of taking part in the charge transfer processes, either by scavenging excited holes or by direct reduction of H+ to H• under UV irradiation. Fermi level equilibrium in the p-n heterojunction suggests the best interparticle charge transfer mechanism explaining how photoinduced electrons with superior energy states and desirable lifetime can be supplied to reduce H+ to H•.

Role of Chalcogens in the Exciton Relaxation Dynamics of Chalcogenol-Functionalized CdSe QD: A Time-Domain Atomistic Simulation

Colloidal CdSe nanocrystals are often stabilized by organic ligands. The choice of such ligands has tremendous detrimental effects on interparticle charge transfer (CT) dynamics in nanocrystalline thin-film devices. It is evident from the recent experiment that photoexcited hole migrates from CdSe quantum dot (QD) to surface-passivating phenyl chalcogenol ligands (PhEH; E = S, Se, Te) at different time scales. But the backward electron–hole (e−h) recombination at the interface remained unexplored. A deep-level understanding of the mechanism of CT at the interface is therefore required to unravel the key role of chalcogen for the betterment of the device performance. Herein, we have performed time-domain density functional theory calculation along with nonadiabatic molecular dynamics (NAMD) simulation to investigate the photoinduced CT at the CdSe–PhEH interfaces. The simulated time scales for hole transfer (HT) are found to follow the trend PhSH > PhSeH > PhTeH that concur excellently with the experimenta...

The Development of Functional Mesocrystals for Energy Harvesting, Storage, and Conversion.

Higher-ordered semiconductors have attracted extensive research interest as an adopted engineering for active solar energy harvesting, storage, and conversion. It is well-known that the effective separation and anisotropic migration of photogenerated charges are the basic driven force required for superior efficiency. However, the morphology and stoichiometric variation of these semiconductors play essential roles in their physicochemical properties of bulk and surface, especially for efficient interparticle or interfacial charge transfer. To this point, the strategy of controlling the topotactic transformation toward superstructures with optimized functionality is preferable for a wide range of optoelectronic and catalytic engineering applications. In this Minireview, we provide an overview of the crystal orientation, synthetic engineering, functional applications, and spatial and temporal charge dynamics in TiO2 mesocrystals and others. The viewpoint of in-depth understanding of the structure-related kinetics would offer an opportunity for design of versatile mesocrystal semiconductors sought-after for potential applications.

ZnO-Photocatalyzed Oxidative Transformation of Diphenylamine. Synergism by TiO2, V2O5, CeO2 and ZnS

Diphenylamine (DPA) undergoes photocatalytic transformation on nanoparticulate ZnO surface yielding N-phenyl-<em>p</em>-benzoquinonimine (PBQ). The reaction rate increases with the increase of (i) DPA-concentration, (ii) ZnO-loading, (iii) airflow rate and (iv) light intensity. The formation of PBQ is larger on using UV-C light instead of UV-A light. The photocatalyst is reusable. The mechanism of the photocatalytic transformation has been discussed with a suitable kinetic law. Nanoparticulate TiO2, V2O5, CeO2 and ZnS enhance the ZnO-photocatalyzed PBQ formation indicating interparticle charge transfer in semiconductor mixtures.

Band alignment and charge transfer pathway in three phase anatase-rutile-brookite TiO2 nanotubes: An efficient photocatalyst for water splitting

The study reports electrochemical synthesis, phase evolution and hydrogen generation efficiency of anatase, anatase-rutile and anatase-rutile-brookite (ARB) TiO2 nanotubes for the first time. The SEM and TEM micrographs confirm the tubular morphology of the samples. The presence of anatase, rutile and brookite phases in a single nanotube is confirmed from high resolution TEM analysis. The water splitting efficiency of the three systems are studied under one sun illumination. It is observed that the anatase-rutile-brookite TiO2 nanotubes are highly efficient compared to anatase-rutile or anatase TiO2 nanotubes. The hydrogen generated by ARB composites, after four hours of one sun illumination, is found to be nearly twice that of anatase TiO2 nanotubes and 1.6 times that of anatase-rutile TiO2 nanotubes. The results suggest that the ARB in single nanotube having two junction interfaces, highly facilitate inter-particle charge transfer compared to single junction anatase-rutile or bare anatase TiO2 nanotubes. From the deconvolution of PL spectra and the synchrotron radiation assisted valence band edge analysis, the band diagram for the anatase-rutile-brookite phase is constructed. The charge separation and its transfer pathway for efficient photo-assisted water splitting are delineated. This opens a new route for the simple synthesis and study of tri-phase TiO2 for efficient photocatalytic water splitting compared to the widely studied two phase TiO2.

Crumpled Cu2O-g-C3N4 nanosheets for hydrogen evolution catalysis

Crumpled cuprous oxide anchored graphitic carbon nitride (Cu2O-g-C3N4) nanosheets were synthesized for photosplitting of water under visible light illumination. The nanosheets were characterized by scanning and transmission electron microscopies, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier Transform Infrared (FT-IR) spectroscopy. The analytical data showed that the surface of g-C3N4 nanosheets crumpled as a result of Cu2O anchoring. The water photosplitting experiments, performed in the presence of a sacrificial agent methanol, showed the liberation of a significant amount of hydrogen, viz., 842μmolh−1g−1 after 48h illumination. Such superior photocatalytic activity may be due to efficient inter-particle charge transfer in the direction from n-type g-C3N4 to p-type Cu2O which hinders the electron-hole recombination.

Self-induced synthesis of phase-junction TiO2 with a tailored rutile to anatase ratio below phase transition temperature.

The surface phase junction of nanocrystalline TiO2 plays an essential role in governing its photocatalytic activity. Thus, facile and simple methods for preparing phase-junction TiO2 photocatalysts are highly desired. In this work, we show that phase-junction TiO2 is directly synthesized from Ti foil by using a simple calcination method with hydrothermal solution as the precursor below the phase transition temperature. Moreover, the ratio of rutile to anatase in the TiO2 samples could be readily tuned by changing the ratio of weight of Ti foil to HCl, which is used as the hydrothermal precursor, as confirmed by the X-ray diffraction analysis. In the photocatalytic reaction by the TiO2 nanocomposite, a synergistic effect between the two phases within a certain range of the ratio is clearly observed. The results suggest that an appropriate ratio of anatase to rutile in the TiO2 nanocomposite can create more efficient solid-solid interfaces upon calcination, thereby facilitating interparticle charge transfer in the photocatalysis.

Enhanced photocatalytic activity of {1 0 1}-oriented bipyramidal TiO2 agglomerates through interparticle charge transfer

Uniformly packed dense TiO2 bipyramid agglomerates (BPA) with the dominantly exposed {101} facets were designed and synthesized by using a simple solvothermal process. From scanning electron microscopy (SEM) image, BPA consists of uniformly and densely packed nanoparticles forming secondary mesopores. BPA structure was intentionally crushed by ball-milling to obtain c-BPA, the photoactivity of which was compared with BPA. The photocatalytic activities of as-prepared BPA and c-BPA were investigated for hydrogen production and 4-chlorophenol degradation and compared with P25 as a reference TiO2. The BPA showed much higher photocatalytic activities than those of c-BPA and P25 (randomly aggregated commercial TiO2 nanoparticles). The marked efficiency improvement in BPA can be ascribed to the noble nanostructural features: (i) the agglomerated bipyramid (BP) units suppressing the electron-hole recombination through efficient interparticle charge transfer, (ii) the well-developed mesopores allowing the efficient diffusion of reactants and products, (iii) the highly {101}-oriented BP units that help efficient charge separation, and (iv) a good crystallinity of the BP units. These superior properties of BPA were also confirmed in their photoelectrochemical behaviors: the electrode of BPA exhibited the highest photocurrent under UV light, the slowest decay of open-circuit potential after turning off the light, and the lowest charge transfer resistance from the electrochemical impedance spectroscopic (EIS) measurement, which implies the retarded recombination of charge pairs and efficient interparticle charge transfer on BPA. The controlled agglomerated structure of the nano-sized TiO2 can enhance the photocatalytic and photoelectrochemical properties through efficient interparticle charge transfer.

Photoinduced oxidative transformation of diphenylamine on CeO2

On the surface of CeO2, diphenylamine (DPA) in ethanol undergoes a photoinduced oxidative transformation yielding N-phenyl-p-benzoquinoneimine (PBQ). The photoinduced transformation of DPA on CeO2 was enhanced by increasing the (i) [DPA], (ii) CeO2-loading, (iii) airflow rate and (iv) photon flux. The formation of PBQ on the CeO2 surface increased due to irradiation at 254nm compared to that observed from irradiation at 365nm. The activity of the CeO2 surface does not decrease during reuse. The photoinduced oxidative transformation mechanism was discussed, and the kinetic law was determined. ZnO and ZnS enhance the photoinduced transformation indicating interparticle charge transfer in semiconductor mixtures.

Enhancement of TiO2-photocatalyzed organic transformation by ZnO and ZnS. Oxidation of diphenylamine

TiO2 anatase photocatalyzes the oxidative transformation of diphenylamine (DPA) to N-phenyl-p-benzoquinonimine (PBQ) in ethanol. The PBQ formation increases with increase of [DPA], TiO2-loading, airflow rate and light intensity. The catalyzed formation of PBQ is larger with UV-C light illumination than with UV-A light illumination. The catalyst is recyclable. The photocatalytic reaction mechanism has been proposed and the kinetic parameters deduced. ZnO and ZnS enhance the TiO2-photocatalyzed DPA oxidation suggesting interparticle charge transfer in mixed semiconductors.

UV irradiation induced transformation of TiO2 nanoparticles in water: aggregation and photoreactivity.

Transformation of nanomaterials in aqueous environment has significant impact on their behavior in engineered application and natural system. In this paper, UV irradiation induced transformation of TiO2 nanoparticles in aqueous solutions was demonstrated, and its effect on the aggregation and photocatalytic reactivity of TiO2 was investigated. UV irradiation of a TiO2 nanoparticle suspension accelerated nanoparticle aggregation that was dependent on the irradiation duration. The aggregation rate increased from <0.001 nm/s before irradiation to 0.027 nm/s after 50 h irradiation, resulting in aggregates with a hydrodynamic diameter of 623 nm. The isoelectric point of the suspension was lowered from 7.0 to 6.4 after irradiation, indicating less positive charges on the surface. ATR-FTIR spectra displayed successive growth of surface hydroxyl groups with UV irradiation which might be responsible for the change of surface charge and aggregation rate. UV irradiation also changed the photocatalytic degradation rate of Rhodamine B by TiO2, which initially increased with irradiation time, then decreased. Based on the photoluminescence decay and photocurrent collection data, the change was attributed to the variation in interparticle charge transfer kinetics. These results highlight the importance of light irradiation on the transformation and reactivity of TiO2 nanomaterials.