Electron-hole Pair Production Research Articles

The electrochemical energy storage and photocatalytic performances analysis of rare earth metal (Tb and Y) doped SnO2@CuS composites

The rational design of composite electrode and catalyst materials is critical for increasing high energy density and structural stability, electron-hole pair production in supercapacitors, and photocatalytic applications. By employing a simple hydrothermal technique, we were able to produce SnO2, CuS, SnO2@CuS, Tb doped SnO2@CuS, and Y doped SnO2@CuS samples. Various analytical techniques such as PXRD, FTIR, UV, SEM, EDS, and XPS examine the synthesized materials' structural, optical, purity, morphology, and binding energy. The fabricated asymmetric Y doped SnO2@CuS/AC device revealed the energy and power densities of 16.2 W h kg−1 and 740 W kg−1 at a current density of 1 A/g, with outstanding cycle stability of 80.9% retention capacitance after 5000 charge–discharge cycles. Furthermore, when exposed to visible light, the Y doped SnO2@CuS catalyst degrades the methylene blue dye with a maximum degradation efficiency of 97%. All of the above results suggested that the obtained Y doped SnO2@CuS material can be utilized in supercapacitor and photocatalytic applications.

Natural Negative-Refractive-Index Materials.

Our calculation shows that negative refractive index (NRI), which was known to exist only in metamaterials in the past, can be found in Dirac semimetals (DSM). Electrons in DSM have zero effective mass and hence the system carries no nominal energy scale. Therefore, unlike those of ordinary materials, the electromagnetic responses of the electrons in DSM will not be overwhelmed by the physical effects related to electron mass. NRI is induced by the combination of the quantum effect of vacuum polarization and its finite temperature correction, which is proportional to T^{4} at low temperature. It is a phenomenon of resonance between the incident light and the unique structure of Dirac cones, which allows numerous states to participate in electron-hole pair production excited by the incident light with a similar dispersion relation to that of Dirac cones. The NRI phenomenon of DSM manifests in an extensive range of photon frequencies and wave numbers and can be observed around the gigahertz range at room temperature.

Simulating 50 keV X-ray Photon Detection in Silicon with a Down-Conversion Layer

Simulation results are presented that explore an innovative, new design for X-ray detection in the 20–50 keV range that is an alternative to traditional direct and indirect detection methods. Typical indirect detection using a scintillator must trade-off between absorption efficiency and spatial resolution. With a high-Z layer that down-converts incident photons on top of a silicon detector, this design has increased absorption efficiency without sacrificing spatial resolution. Simulation results elucidate the relationship between the thickness of each layer and the number of photoelectrons generated. Further, the physics behind the production of electron-hole pairs in the silicon layer is studied via a second model to shed more light on the detector’s functionality. Together, the two models provide a greater understanding of this detector and reveal the potential of this novel form of X-ray detection.

Analytical WKB theory for high-harmonic generation and its application to massive Dirac electrons

We propose an analytical approach to high-harmonic generation (HHG) for nonperturbative low-frequency and high-intensity fields based on the (Jeffreys-)Wentzel-Kramers-Brillouin (WKB) approximation. By properly taking into account Stokes phenomena of WKB solutions, we obtain wave functions that systematically include the repetitive dynamics of production and acceleration of electron-hole pairs and quantum interference due to phase accumulation between different pair production times (St\"uckelberg phase). Using the obtained wave functions without relying on any phenomenological assumptions, we explicitly compute electric current (including intra- and interband contributions) as the source of HHG for a massive Dirac system in $(1+1)$ dimensions under an ac electric field. We demonstrate that the WKB approximation agrees well with numerical results obtained by solving the time-dependent Schr\"odinger equation and point out that the quantum interference is important in HHG. We also predict in the deep nonperturbative regime that (1) harmonic intensities oscillate with respect to electric-field amplitude ${E}_{0}$ and frequency $\mathrm{\ensuremath{\Omega}}$, with a period determined by the St\"uckelberg phase, (2) the cutoff order of HHG is determined by $2e{E}_{0}/\ensuremath{\hbar}{\mathrm{\ensuremath{\Omega}}}^{2}$, with $e$ being the electron charge, and that (3) noninteger harmonics, controlled by the St\"uckelberg phase, appear as a transient effect. Our WKB theory is particularly suited for a parameter regime, where the Keldysh parameter $\ensuremath{\gamma}=(\mathrm{\ensuremath{\Delta}}/2)\mathrm{\ensuremath{\Omega}}/e{E}_{0}$, with $\mathrm{\ensuremath{\Delta}}$ being the gap size, is small. This parameter regime corresponds to intense lasers in the terahertz regime for realistic massive Dirac materials. Our analysis implies that the so-called HHG plateau can be observed at the terahertz frequency within the current technology.

Designing of highly active g-C3N4/Sn doped ZnO heterostructure as a photocatalyst for the disinfection and degradation of the organic pollutants under visible light irradiation

The use of nanocomposites having heterostructured junctions-nanoparticle combination for enhanced photocatalytic degradation ability is in practice. These nanocomposites were considered better photocatalysts due to increased electron-hole pair production and delay in their recombination rate. Thus, photogenerated electron-hole pairs were also reported to be used as good antibacterial agents. In this study, a series of g-C3N4 hybridized with Sn doped ZnO novel nanocomposites were prepared using the unique chemical co-precipitation method. This synthesis method was known as a low-cost, environmentally-friendly, in-situ fabrication process. Zinc acetate, Tin chloride, and urea are being used as precursor materials. The morphology of synthesized g-C3N4 hybridized with Sn doped ZnO nanocomposite was mainly assessed by XRD, FTIR, TEM, and SEM techniques. The elemental determination was performed by using EDS analysis, and band gaps were calculated using the tauc plot method. The photocatalytic ability of synthesized materials was established by photodegradation of methylene blue (MB) dye under sunlight irradiation. To establish reactive oxygen species involved in the photocatalytic mechanism, a series of scavenger experiments were conducted. It was discovered that both O2− and h+ radicals are involved in photodegradation and antibacterial activity. The visible light cropping was assessed by using PL spectroscopy. The surface area calculations were made via BET analysis. The antibacterial properties were assessed against Escherichia Coli, Bacillus subtilis, Staphylococcus aureus, and Staphylococcus saliverius.

Efficiency limitation of thin film coated planar semiconductor thermal neutron detector

Semiconductor thermal neutron detectors are increasingly been used in in-core thermal neutron flux measurements in nuclear reactors. One limitation of these detectors is that they suffer from low detection efficiency. In this work, the maximum efficiency of a planar structure thermal neutron detector was determined using two widely used computer codes: Geant4 and MCNP6. Diamond and SiC are used as based materials in this work because of their large electron-hole pair production efficiency which generally translates to high detection efficiency. The electron-hole pair production efficiency is the fraction of energy that goes into electron-hole pair creation and depends on the band-gap energy and the W-values. These two materials are also not susceptible to radiation damage which makes them suitable for high radiation environments such as nuclear reactors. Thermal neutron detection is achieved using 10B and 6LiF conversion layers coated on the surface of the detector. The maximum efficiency for 10B conversion layer was achieved at a thickness of 2 μm. The efficiency at this thickness is 5.57 ± 0.09% and 5.49±0.09% for diamond and silicon carbide, respectively. When 6LiF was used as a thermal neutron conversion layer, the maximum thickness of the conversion layer was determined to occur at 17 μm. The efficiency at this thickness is 5.47 ±0.06% and 5.38±0.06% for diamond and SiC, respectively.

Design of Metal@Titanium Oxide Nano-heterodimers by Laser-Driven Photodeposition: Growth Mechanism and Modeling.

In order to circumvent the usual nucleation of randomly distributed tiny metallic dots photodeposited on TiO2 nanoparticles (NPs) induced by conventional UV lamps, we propose to synthesize well-controlled nanoheterodimers (NHDs) using lasers focused inside microfluidic reactors to strongly photoactivate redox reactions of active ions flowing along with nanoparticles in water solution. Since the flux of photons issued from a focused laser may be orders of magnitude higher than that reachable with classical lamps, the production of electron-hole pairs is tremendously increased, ensuring a large availability of carriers for the deposition and favoring the growth of a single metallic dot as compared to secondary nucleation events. We show that the growth of single silver or gold nanodots can be controlled by varying the beam intensity, the concentration of the metallic salt, and the flow velocity inside the microreactor. The confrontation to a build-in model of the metallic nanodot light-induced growth onto the surface of TiO2 NPs shows the emergence of a predictable "master behavior" on which individual growths obtained from various tested conditions do collapse. We also characterized the associated quantum yield. Eventually, we successfully confronted our model to growth data from the literature in the case of silver on TiO2 and gold on II-VI semiconducting NPs triggered by UV lamps. It shows that for the photosynthesis of NHDs the efficiency of the electron-hole pair production rate matters much more than the number of pairs produced and that the use of laser light can provide a photodeposition-based synthesis at the nanoscale.

Synthesis and characterization of Eu3+ doped TiO2 thin films deposited by spray pyrolysis technique for photocatalytic application

In this study, nanocrystalline TiO2: Eu3+ thin films are successfully formed by spray pyrolysis technique deposited on glass substrate. Structure, optical, electrical, surface morphology, and photocatalytic degradation of Methylene blue have been examined. The XRD analysis illustrate the tetragonal crystal structure of films with anatase phase and reduces crystallite size linearly with increasing Eu3+ concentration. The optical properties of the films are analyzed using transmittance and reflectance spectra, which are measured using UV–vis-NIR double-beam spectrophotometer. Optical properties such as refractive index (n), extinction coefficient (k), optical conductivity (σ) and Urbach energy (Eu) have been calculated as a function of Eu3+ concentration. Film thickness were evaluated using the refractive index dependence on wavelength. The films thickness were determined as 97.13, 122.62, 123.24, 117.14 and 128.25 nm, respectively, for Eu doped TiO2 at 0,4, 6, 8 and 10 wt % doping concentration. The band gap values raised from 3.29 to 3.42 eV with increasing the Eu3+ dopant concentration. The highest electrical conductivity was found to be 3.01 × 10−2(Ω·cm)−1 at high doping level with 10 wt% Eu3+. Scanning electron microscopy (SEM) analysis indicated consistent allocation of irregular and spherical shaped grains covering the substrate surface. The average grain size in range of 82.5—51.1 nm is observed and films show porous nature. The photocatalytic effect of TiO2: Eu3+ thin films is predicted from the degradation of methylene blue (MB) at room temperature under UV light irradiation. An enhancement in photocatalytic degradation observed by increasing the amount of Eu3+ due to increase in the (electron-hole) pair production and increase of film thickness. These results make TiO2: Eu3+ thin films as attractive candidate for photovoltaic cells and other optoelectronic device applications.

Synthesis of enriched boron nitride nanocrystals: A potential element for biomedical applications

The shortcomings in Boron neutron capture therapy (BNCT) and Hyperthermia for killing the tumor cell desired for the synthesis of a new kind of material suitable to be first used in BNCT and later on enable the conditions for Hyperthermia to destroy the tumor cell. The desire led to the synthesis of large band gap semiconductor nano-size Boron-10 enriched crystals of hexagonal boron nitride (10BNNCs). The contents of 10BNNCs are analyzed with the help of x-ray photoelectron spectroscopy (XPS) and counter checked with Raman and XRD. The 10B-contents in 10BNNCs produce 7Li and 4He nuclei. A Part of the 7Li and 4He particles released in the cell is allowed to kill the tumor (via BNCT) whereas the rest produce electron-hole pairs in the semiconductor layer of 10BNNCs suggested to work in Hyperthermia with an externally applied field.

Synthesis, characterization and photocatalytic parameters investigation of a new CuFe2O4/Bi2O3 nanocomposite

Synthesis of heterojunctions to improve the efficiency of photocatalyst and charge-transfer properties has been a major concern recently. A novel photocatalyst copper ferrite-bismuth oxide (CuFe2O4/Bi2O3) nanocomposite was synthesized with unique magnetic properties. In this nanocomposite catalyst, the nano-petals of bismuth oxide (Bi2O3) were entangled with CuFe2O4 particles via the ultra-sonication method. The structure of as-synthesized samples was investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), whereas the morphology and optical band gap was determined using field emission scanning electron microscopy (FESEM) and UV–Vis spectrophotometry. Comparative photocatalytic activity of copper ferrite and the nanocomposite was examined for the degradation of Methylene Blue (MB) dye. The superior performance of photocatalyst is attributed to the visible light sanitizer; CuFe2O4 could assist Bi2O3 to absorb more photons of incident light which promotes the production of photoexcited electron-hole pairs. Additionally, the catalyst could be recycled and separated from the dye without any loss of photocatalytic efficiency owing to good chemical stability as well as magnetic separation.

Current sources based on supercapacitors with β-active isotopes

In asymmetric supercapacitors, electric charges are separated and accumulated in conditions of neutron irradiation. The paper presents the results of studying current sources with radioactive isotopes (CSRI) based on supercapacitors of 100 F made by neutron activation of the elements of the substances (BN or SrO) introduced to the electrodes. Following the neutron irradiation with a dose of up to 400 Gy, the supercapacitors turn into CSRIs and have a charging rate of up to 7.8 μV/day. The CSRI charging rate increases in proportion to the activation with a neutron dose up to 14 kGy. This is explained by the production of β-active isotopes as a result of the 14N(n, p)14C and 88Sr(n, γ)89Sr reactions in the supercapacitor electrode materials. Estimation of the radiation-induced charge accumulation rate, with regard for the energy released during β-decay of 14C and 89Sr, excludes the known mechanisms of charge separation in a condensed environment due to the ionization and production of secondary electrons, the production of electron-hole pairs, etc. The electric charge separation and accumulation in CSRIs take place as a result of non-equilibrium thermoelectric phenomena in the near-electrode nanoregions. Nuclear reactions in nanoscale regions produce “temperature gradients” of up to 105 K/nm, this leading to up to 1013 electrons “evaporating” from nanocrystallites at times of ~ 10-11 s.

Enhanced photocatalysis performance of mechano-synthesized V2O5–TiO2 nanocomposite for wastewater treatment: Correlation of structure with photocatalytic performance

The harmful chemical organic dyes used in textile industries and wastewater posses a great threat to human beings due to huge toxicity and enormous health hazards. Consequently, the conversion of these harmful chemicals into harmless substances becomes utmost essential for sustainable development in wastewater research. High-energy ball-milling of orthorhombic V2O5-anatase (a) TiO2 mixture (1:1 M ratio) at room temperature results in the formation of nanocrystalline V2O5–TiO2 solid solution phase. A series of V2O5–TiO2 solid solution is synthesized by varying the milling time from 5min to 20h. The Rietveld X-ray powder structure refinement methodology has been adopted for microstructure characterization of unmilled and all ball-milled nanocomposite samples, in terms of lattice imperfections. From Rietveld analysis, lattice parameters, relative phase abundance of individual phases, crystallite size and r.m.s. lattice strain values are estimated. At the early stage of milling of 30min, a-TiO2 transforms to polymorphic rutile (r)-TiO2 due to high energy impact of mechanical alloying. The final ball-milled powder mixture is composed of V2O5–TiO2 solid solution with a trace amount of r-TiO2 phase. Photocatalytic study through the degradation of Rhodamine B (RhB) in presence of visible light reveals enhanced degradation (~94%) of RhB with 3h ball-milled V2O5–TiO2 nanocomposite, compared to ~74% with 15h milled nanocomposite reported earlier. Optical bandgaps of ball-milled V2O5–TiO2 nanocomposites are within the semiconducting range. FESEM study of ball-milled powder mixture reveals the pineapple flower-like morphology of nanoparticles of V2O5–TiO2 nanocomposites. An enormous number of the leaf (V2O5)/flower (TiO2) semiconducting heterojunctions with small crystallite size and higher surface area are believed to excel the photocatalytic performance of the nanocomposite through electron-hole pair production and easy electron transport mechanism between valance and conduction bands due to low bandgap energy of TiO2 with the addition of V2O5. TEM study further reveals the particle size distribution and confirms the presence of crystalline phases in the ball-milled nanocomposite. FTIR spectrum of 3h ball-milled V2O5–TiO2 in RhB solution corroborates the photocatalytic property of the prepared nanocomposite. Finally, an attempt has been made to establish a correlation between structure/microstructure and photocatalytic performance of the nanocomposites.

Transport model for a transverse electron beam-pumped semiconductor laser

AbstractA transport model for a transverse electron beam-pumped semiconductor laser has been developed. The model incorporates spatial dependencies of the power deposition from the beam as well as a three-dimensional model of the gain medium and the field intensity of the photons produced by stimulated emission in the oscillation cavity. This model accounts for spatial inhomogeneities and has been solved for a variety of pumping strengths. The model was developed so that it can be benchmarked with electron beam pumping. The dominant mechanisms for the production of electron–hole pair production within the semiconductor material is similar to the dominant mechanisms for the production of electron–hole production using ion beams. Thus, the model can be extended to fission fragment ion pumping of semiconductor lasers in order to model a nuclear-pumped laser/reactor system.

Synthesis and characterization of Ag/TiO2/composite aerogel for enhanced adsorption and photo-catalytic degradation of toluene from the gas phase

Despite titanium dioxide has some remarkable properties as a photo-catalyst, its usage in the photo-catalysis processes is associated with several drawbacks, like high band gap energy and clumping of its particles. In this study, a composite aerogel was exploited as a support for titanium dioxide to prevent clump formation and increase the production of electron-hole pairs. The results revealed that both utilized nanoparticles, i.e. TiO2 and Ag, were uniformly dispersed on the surface of composite aerogel. The absorption region of the synthesized catalysts shifted to the visible region and, in fact, the additions of Ag to the composite aerogel reduce the band gap energy of TiO2 from 3.17 to 2.7 eV. Studies on the degradation of toluene in gas streams through a fluidized bed reactor showed that the photo-catalytic activity of TiO2 supported on the composite aerogel was much higher than that of the unsupported titanium dioxide, so that the degradation rates of toluene were 95.7% and 15%, respectively for supported and unsupported TiO2. The results indicated that the highest oxidation rate of toluene was obtained at 45% humidity. The Intermediate products formed during the degradation of toluene by the composite photo-catalyst were identified which were included formic acid, acetic acid, and benzaldehyde. Overall, the composite aerogel could be used as a useful support for the TiO2 catalyst, and the prepared photo-catalyst has a high potential to be used in the oxidation of toluene in gas-phase streams in industrial scale.

Sono-solvothermal hybrid fabrication of BiOCl-Bi24O31Cl10/rGO nano-heterostructure photocatalyst with efficient solar-light-driven performance in degradation of fluoroquinolone antibiotics

Herein, novel BiOCl-Bi24O31Cl10/rGO heterostructured nanocomposites with various contents of rGO were designed through a simple sono-solvothermal method, employing in the photo-elimination of fluoroquinolone antibiotics under the simulated solar-light. Their properties were described using various analyses such as XRD, Raman spectroscopy, FESEM, HRTEM, surface particle size distribution, BET-BJH, DRS and photoluminescence analyses. The results revealed the suitable dispersion of BiOCl-Bi24O31Cl10 nanoparticles on the rGO nanosheets and the creation Bi-C bonds in BiOCl-Bi24O31Cl10/rGO. On the basis of experimental outcomes, it was concluded the strong influence of the rGO value into BiOCl-Bi24O31Cl10/rGO structure on the fluoroquinolone photo-degradation and the high photo-activity was obtained on the BiOCl-Bi24O31Cl10/rGO(0.5%) with the elimination rate constant 1.6 times contrasting to the bare BiOCl-Bi24O31Cl10 in the ofloxacin photo-removal. This consequence was devoted the decrease of band gap and the enhanced light absorption features which can lead to enhancing production of electron-hole pairs, the raising separation and transmission of charge carriers and reducing recombination rate of them, the increasing surface adsorption of contaminant molecules and the increment of accessible active sites. Besides, the synthesized BiOCl-Bi24O31Cl10/rGO(0.5%) was exposed the great stability.

Atomic layer deposition of ZnO thin film on surface modified monolayer MoS2 with enhanced photoresponse

Monolayer MoS2 was grown on a sapphire substrate by CVD, and then transferred to a silicon wafer substrate. The morphology and crystalline of the MoS2 were characterized by AFM, SEM, and XRD. After perylene-3,4,9,10-tetracarboxylic acid (PTCA) surface treatment on the MoS2, a continuous layer of ZnO thin film was deposited. Finally, the photoresponse of both ZnO and ZnO/MoS2 thin films was investigated, and the ZnO/MoS2 thin film showed enhanced photoresponse over pure ZnO thin film. The higher response of ZnO/MoS2 hetero-structure could be attributed to the effective charge transfer between ZnO and MoS2 surface and the re-absorption of light photon resulting in the production of electron-hole pairs.

(Invited) Light Enhanced Metal Assisted Chemical Etching of Silicon

The study of electrochemicl porosification of silicon has allowed the production of different kinds of porosities in it, ranging from micropores to macropores, and directed by cristallographic planes, or electrical current lines. Additional studies have been on the use of different kinds of electrolytes, to etch faster, or with lower branching. Pore modulation has been also an important development, for a range of applications from photonics to energy storage devices. The modulation can be of either different porosities or different pore diameters, and has been accomplished by the use of different current densities [1], or by the use of different light intensities (mainly for n-type Si) [2]. In particular, the use of light allows the production of electron-hole pairs in semiconductors. This is necessary in n-type Si, since electronic holes are part of the etching reaction, and they are scarce in n-type wafers. Having the availability of more of fewer electronic holes, one can etch wider or narrower pores respectively [1]. Metal Assisted Chemical Etching (MACE) is an alternative etching method, which does not use a power source (it is an electroless method). Nobel metal (commonly Au, Ag or Pt) particles or films are deposited on the surface of Si, and the metallized samples are immersed in an etching solution afterwards. The regions with metal are commonly etched much faster, thus they work as a catalyst [3]. At the metal-semiconductor interface, space-charge-region (SCR) is formed, accelerating electronic holes formed at the electrolyte-metal interface. In this way, there is a higher availability of holes for etching in (or close to) the regions where the metal is present. Having an internal electric field (given by the SCR) in MACE, which is external in the case of electrochemical etching, it is strightforward to think that light may work in a similar way in both etching methods. However, there are just a few reports on the use of light for MACE, and it has been used just at the front-side (the etched face). There are no reports on the use of back-side illumination for MACE. In the present work, evidences of pore modulation or etching conditions through the use of alternating illumination at the back-side will be presented. Illumination induces either lateral or vertical etching, depending on the doping type of Si. [1] E. Quiroga-González, J. Carstensen, C. Glynn, C. O’Dwyer, H. Föll, Phys.Chem.Chem.Phys., 16, 255 (2014). [2] S. Matthias, F. Müller, J. Schilling, U. Gösele, Appl. Phys. A, 80(7), 1391 (2005). [3] X. Li and P.W. Bohn, Appl. Phys. Lett.77, 2572 (2000).

Photoexcitation Cascade and Quantum-Relativistic Jets in Graphene.

In Dirac materials linear band dispersion blocks momentum-conserving interband transitions, creating a bottleneck for electron-hole pair production and carrier multiplication in the photoexcitation cascade. Here we show that the decays are unblocked and the bottleneck is relieved by subtle many-body effects involving multiple off-shell e-h pairs. The decays result from a collective behavior due to simultaneous emission of many soft pairs. We discuss characteristic signatures of the off-shell pathways, in particular the sharp angular distribution of secondary carriers, resembling relativistic jets in high-energy physics. The jets can be directly probed using solid-state equivalent of particle detectors. Collinear scattering enhances carrier multiplication, allowing for emission of as many as ∼10 secondary carriers per single absorbed photon.

High photocatalytic performance of carbon quantum dots/TNTs composites for enhanced photogenerated charges separation under visible light

A novel high-efficiency composite photocatalyst, carbon quantum dots (CQDs) are embedded onto out-surface surface of the TiO2 nanotubes (TNTs) with high percentage of photocatalytic reactive facets, was fabricated through an improved hydrothermal method. The characterization results showed that the CQDs was chemically adhered to out-surface of the TNTs through the CO and/or CO bonds formed between the CQDs and TNTs. The photocatalytic performance of as-prepared photocatalysts was evaluated to degrade methylene blue (MB) solution under the visible light. The as-prepared photocatalysts had a marvelous photocatalytic performance and the CQDs/TNTs-0.2 sample had the best photocatalytic performance with a decolorization rate of 91.3% and approximately 2 times more than that of pure TNTs for the high initial concentration of MB solution (30 mg/l) within 50 min under visible-light irradiation. The CQDs with excellent Up-Conversion Photoluminescence(UCPL)properties as co-catalysts can covert long wavelength light (>600 nm) absorbed from infrared light into visible light (<600 nm), which activates the TNTs to produce electron-hole pairs. Moreover, the CQDs also can capture the photoexcited electrons and prolong the lifetime of the photoexcited charges. In addition, the stacking interaction of the π-π bonds between the CQDs and the dyes of the benzene ring structure would be beneficial for enhancing the absorption performance of the CQDs/TNTs photocatalysts. The photocatalytic mechanism and process have also been discussed in detail according to the characterization and photodegradation results. This work is of great interest to introduce a new visible-light photocatalyst for the treatment of organic wastewater and protect environment.

The synergy of SPR effect and Z-scheme of Ag on enhanced photocatalytic performance of 3DOM Ag/CeO2-ZrO2 composite

Using polystyrene spheres (PS) as a template, a kind of three-dimensionally ordered macroporous (3DOM) Ag/CeO2-ZrO2 material was synthesized by the sol–gel combined with the decompression filling method. A series of characterization methods, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (UV–vis/DRS), Scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HR-TEM), and N2 adsorption–desorption measurements were used to study its composition, structure, morphology, and surface physicochemical properties. The synthesized composite material 3DOM Ag/CeO2-ZrO2 shows a good crystal structure, open and transparent arrangement in a three-dimensional space. Meanwhile, compared with the sample without PS treatment, the composite material has a smaller band gap energy value, which means under the excitation of light, it is easier to produce electron–hole pairs and enables to absorb more reactive molecules on the surface of the catalyst, thus improving the photocatalytic performance of the composite. And after loading Ag metal on the composite, the light absorption of the catalyst is extended to the visible region by the surface plasmon resonance effect (SPR), resulting in promoting the absorption efficiency of light. During multimode photocatalytic degradation experiments of Congo Red (CR), 3DOM Ag/CeO2-ZrO2 composite exhibited an excellent photocatalytic performance. Under ultraviolet light, its catalytic performance was much better than that of both commercial catalyst P25 and the sample without loading Ag. At the same time, in the photocatalytic hydrogen evolution experiment, 3DOM Ag/CeO2-ZrO2 showed a stronger ability of water splitting into hydrogen, whose hydrogen yield (53 μmol in 8 h) was about 4 times than that of P25, indicating 3DOM Ag/CeO2-ZrO2 had the ability of photodegradation and photolysis of water. In addition, superoxide free radical (O2−), hydroxyl radical (OH), and hole (h+) were considered as main reactive groups in the photocatalytic process according to capture experimental results. Moreover, the transfer effect of Ag as Z-Scheme in the photocatalytic reaction was speculated as well.