Light Absorption Region Research Articles

Charge separation effect in the nanocomposites of Co3O4-QDs: visible light photocatalytic dye degradation in aqueous solutions.

Photo-treatment of water is a promising environmentally friendly process that provides clean water and makes wastewater reusable in industry. Thus, efforts toward finding highly efficient photocatalysts have gained a huge attention to remove the organic contaminants in water. Quantum dots (QDs) are extensively utilized for photocatalytic remediation regarding their prominent optical, electrical, and chemical properties. Herein, we report the highly efficient and environmentally friendly synthesis of Co3O4-QDs-based graphene quantum dots (GQDs) and infinite coordination polymer comprising Zn nodes (Zn-ICP) nanocomposites as active and robust photocatalysts for photo-assisted water treatment. The pristine Co3O4-QDs, GQDs, and Zn-ICP showed lower activity under visible light. However, after functionalization of GQDs and Zn-ICP with Co3O4-QDs, the activity increased, and more photocatalytic efficiency was achieved. For instance, Zn-ICP, GQDs, Co3O4-QDs, Co3O4-QDs/Zn-ICP, and Co3O4-QDs/GQD degraded 21, 19, 52, 73, and 83% of rhodamine B (RhB) and 34, 46, 50, 73, and 76% of methylene blue (MB) after 60min. The high photocatalytic efficiency was ascribed to the conjugation of Co3O4-QDs with GQDs and Zn-ICP which causes efficient absorption of visible light. The existence of Co3O4-QDs was found to be essential not only for effective charge separation but also widening the region of light absorption followed by increase in photocatalytic performances. Charge separation in photocatalytic reactions, energy levels of nanocomposites, and mechanism of the photocatalytic process were investigated by photoluminescence spectra (PL), Mott-Schottky, electrochemical impedance (EIS), and diffuse reflectance UV-Vis spectroscopy (DRS).

Performance enhancement of α-Fe2O3@Bi2S3 heterojunction for photocathodic protection of 304SS

Hematite (α-Fe2O3) is one of the most promising candidates as a photoanode for photocathodic protection (PCP) of 304SS. However, serious charge recombination has hindered the application. In this work, we verified the feasibility of constructing heterojunction for enhancing the PCP performance. α-Fe2O3@Bi2S3 can not only broaden the solar light absorption region but also provide a built-in electric field to improve charge separation and close junctions for charge transport. When α-Fe2O3@Bi2S3 was coupled with 304SS, the OCP under illumination negatively shifted to −0.788 VAg/AgCl, which was ca. 600 mV negative than the corrosion potential of 304SS. The photoinduced current density reached 32 μA cm−2, outperforming the bare Bi2S3 and α-Fe2O3. The formation of a type II heterojunction between Bi2S3 and α-Fe2O3 was proposed and verified by the electrochemical impedance measurements.

Photoelectrochemical Antibacterial Platform Based on Rationally Designed Black TiO2-x Nanowires for Efficient Inactivation against Bacteria.

A hyphenated strategy for photoelectrochemical (PEC) disinfection is proposed with rationally designed black TiO2-x as a photoresponsive material. The PEC method, a fusion of electrochemistry and photocatalysis, is an innovative and effective way to improve photocatalytic performance, which imparts certain properties to the photoelectrode and greatly promotes the charge transfer, thus effectively inhibiting the recombination of carriers and greatly promoting the catalytic efficiency. The oxygen vacancy (Vo) engineering on TiO2 is conducted to obtain black TiO2-x, which shows a much larger light absorption region in the full solar spectrum than the pristine white TiO2 and presents excellent PEC sterilization performance. The bactericidal efficiency with the PEC method is 10 times higher than that with the photocatalytic method, inactivating 99% of bacteria within a short time of 30 min. In addition, the black titanium oxide nanowires (B-TiO2-x NWs) are grown on flexible carbon cloth (CC) to form a sandwich structural self-cleaning face mask. The bacteria adhering to the surface of the mask will be sterilized quickly and efficiently under the illumination of visible light. The face mask with the characteristics of superior antibacterial effect and long service lifetime will be used for epidemic prevention and reduce the second pollution.

Two-dimensional polar materials for photocatalytic water splitting

<p indent="0mm">As one of the most charming and attractive technologies, photocatalytic overall water-splitting using solar energy is known as a feasible and efficient route to alleviate energy crisis and environmental pollution. Since the seminal work of photocatalytic decomposition of H₂O into H₂ and O₂ on a Pt/TiO₂ electrode by Fujishima and Honda in 1972, photocatalytic water splitting has been persistently investigated, achieving many remarkable advancements. In principle, photocatalytic water splitting reaction mainly involves the following fundamental processes: Absorption of photons induces electron transition and forms electron-hole pairs; then the photogenerated electron-hole pairs separate and migrate to the surface of the photocatalyst; finally, redox reaction occurs on the surface. Therefore, to develop high-performance photocatalysts, several criteria must be fulfilled, including a moderate band gap that should be larger than <sc>1.23 eV</sc> but lower than <sc>3.0 eV</sc> to maximize absorption and utilization solar light, the ability of rapid separation and transfer of carriers, and the suitable band edge alignment to straddle the redox potentials of water. To this end, numerous efforts have been devoted to searching for photocatalytic candidates. In recent years, two-dimensional (2D) materials, e.g., g-C₃N₄, phosphorene and transition-metal dichalcogenides, have been identified as the potential photocatalysts candidates for water splitting. Compared with the bulk materials, 2D materials hold excellent ability of optical adsorption, short carrier migration distance, high carrier mobility, large specific surface area, and abundant active sites. Therefore, the 2D materials are desirable for high-performance photocatalysts. Nevertheless, most of the 2D photocatalysts for water splitting have the structural symmetry along the out-of-plane direction, which mainly harvests the ultraviolet light and limits the efficiency of solar energy utilization. Some new materials and mechanisms for photocatalytic water-splitting are urgently needed. Interestingly, the asymmetric 2D materials with the intrinsic dipole moment, termed as 2D polar materials, show exciting prospects for the photocatalytic applications with high efficiency. The intrinsic dipole moment in 2D polar materials not only accelerates the separation of photogenerated carriers but also is good for relieving the conventional restriction of <sc>1.23 eV</sc> for band gap of photocatalysts, leading to a widened light absorption region (from visible to near-infrared light). Thus, the solar energy utilization efficiency will be substantially enhanced. Motivated by this mechanism, some 2D polar photocatalysts are proposed, such as MXY (M=W, Mo, Cr, Pt; X, Y=S, Se, Te, X<x content-type="symbol">¹</x>Y), M₂XY (M=Ga, In; X, Y=S, Se, Te, X<x content-type="symbol">¹</x>Y), and M₂X₃(M=Al, Ga, In; X=S, Se, Te). In this review, we outline the recent progress in material discovery and photocatalytic characteristics of the different types of 2D polar photocatalysts, including Janus materials and ferroelectrics. The underlying mechanisms for polarization-promoted photocatalysis are discussed to better understand the role of 2D polar materials in photocatalysis. After the presentation of the experimental efforts on 2D polar materials, we conclude with a discussion of the emerging challenges and new perspective for future research and development on 2D polar photocatalysts. We hope that this review, with a specific focus on 2D polar photocatalysts, would help readers gain deep understandings on 2D polar material-based photocatalysts and in turn stimulate further both theoretical and experimental efforts.

Comprehensive investigation on robust photocatalytic hydrogen production over C3N5

Carbon nitride has drawn numerous eyes in the past decade, whereas the photocatalytic performance is significantly limited by its wide band-gap (∼2.7 eV for C 3 N 4 ) simultaneously. Recently, C 3 N 5 with narrower band-gap has been reported, however, a systematically investigation on its photoactivity for H 2 production has not been reported. The present work demonstrates the synthesis of C 3 N 5 by thermal treatment of 3-amino-1,2,4-triazole, and the photocatalytic performance for H 2 production of C 3 N 5 is investigated comprehensively. Photocatalytic H 2 production rate of C 3 N 5 is ∼2.2 times higher than that of C 3 N 4 with 1.0 wt% Pt as co-catalyst, and series of experiments are carried out to explore the behind elements accounting for the high photoactivity. Combining the results of DRS, PL and photocurrent, it is found that C 3 N 5 possesses wider visible light absorption region, lower band-gap and quicker photogenerated e - /h + separation efficiency. Moreover, characterizations including in-situ DRIFTS are adopted to monitor the adsorption property of H 2 O on C 3 N 5 , which plays a significant role in surface water reduction reaction, and higher amount of adsorbed H 2 O molecules on C 3 N 5 is confirmed. The present work exhibits new insights into the high photocatalytic performance of N-rich carbon nitride catalysts. As a new type of carbon nitride, C 3 N 5 exhibits much higher photocatalytic H 2 production activity than conventional C 3 N 4 , which represents a new direction for designing materials for photocatalytic applications.

Photocatalytic Activity of TiO2-Doped Fe, Ag, and Ni with N under Visible Light Irradiation.

Doping with noble metal ions or doping with nitrogen has been attempted to prepare TiO2 that reacts even in visible light. In this study, TiO2 was doped with nitrogen and various metal ions instead of noble metals. The TiO2 photocatalysts doped with metal ions (Fe, Ag, Ni) and nitrogen were prepared by a sol-gel method. Their physicochemical properties were characterized and their photocatalytic activities were investigated under visible light irradiation. In TiO2 doped with metal ions and nitrogen, the light absorption region was extended to visible light. The photoluminescence intensity was much greater in N/Ni/TiO2 than in N/Ag/TiO2 and N/Fe/TiO2. The photolysis activities of N/Ni/TiO2 were the highest in formaldehyde decomposition and methylene blue decomposition. The sterilization efficiency of N/Ni/TiO2 was the highest in the evaluation test for the inhibition of the proliferation of Pseudomonas aeruginosa. The bandgap of N/Ni/TiO2 was 2.4 eV, which was significantly lower than that of anatase TiO2 (3.2 eV). The N/Ni/TiO2 had a much higher optical intensity than other metal ion-doped TiO2, so it was highly active under visible light irradiation.

A novel CoSeO3 photocatalyst assisting g-C3N4 in enhancing hydrogen evolution through Z scheme mode

A novel CoSeO3/g-C3N4 composite photocatalyst with Z-scheme heterostructure is constructed through electrostatic self-assembly to be utilized in photocatalytic hydrogen evolution. The optimal photocatalytic H2 evolution rate of CoSeO3/g-C3N4 hybrids and apparent quantum yield (AQY) have raised about 65.4 times under full light irradiation with no noble metal cocatalyst loading than that of pure g-C3N4. The CoSeO3 semiconductor is firstly prepared for assisting to elevate the photocatalytic hydrogen evolution activity. After combining with g-C3N4, CoSeO3/g-C3N4 hybrids with a sheet-sheet structure enhance the contact area with water and broaden the light absorption region as well as reduce transfer resistance of carriers. Moreover, the photo generated carriers possess a typical direct Z scheme transmission, which decreases the recombination of electrons and holes. This work offers a new choice for constructing a Z scheme heterostructure to apply in photocatalytic water reduction, and offers a deep view to explain the elevated photocatalytic activity.

Fabrication of a La-doped BiVO4@CN step-scheme heterojunction for effective tetracycline degradation with dual-enhanced molecular oxygen activation

• Both La doping and La-BiVO 4 @CN heterojunction promoted electron-hole separation. • Dual methods for O 2 − formation have been achieved by heterojunction and La doping. • O 2 − and h + were determined to be dominant active species for TC degradation. • La-BiVO 4 @CN revealed boosted visible-light photocatalytic TC degradation rate. • A possible photocatalytic mechanism of the S-scheme La-BiVO 4 @CN was proposed. A self-assembly method has been used to construct g-C 3 N 4 -nanosheets (CNNS)-wrapped lanthanum-doped bismuth vanadate (La-BiVO 4 @CN) heterojunction. The interaction between La-BiVO 4 and CNNS could broaden the light absorption region and facilitate photogenerated carrier separation and interfacial charge transfer. Theoretical and experimental results proved that the enhancement of the photocatalytic activity was ascribed to the following two reasons: (i) La atoms could localize excess electrons and adsorb free O 2 to promote the formation rate of superoxide radical ( O 2 − ) in photocatalyst, (ii) La-BiVO 4 @CN, S-scheme heterojunction photocatalyst, could further overcome the photo-induced charge carriers of BiVO 4 with poor redox ability, activated the dissolved oxygen to create more reactive oxygen species (ROS) with high oxidation capacity, which was beneficial for photocatalytic activity. La-BiVO 4 @CN also exhibited better recyclability after five cycles. Meanwhile, this work clarified the charge carriers transport pathway and proposed the photocatalytic reaction mechanism, providing a feasible strategy to design oxidation catalysts by increasing reactive oxygen species generation.

Ag-decorated GaN for high-efficiency photoreduction of carbon dioxide into tunable syngas under visible light

Visible light-driven photoreduction of CO2 and H2O to tunable syngas is an appealing strategy for both artificial carbon neutral and Fischer–Tropsch processes. However, the development of photocatalysts with high activity and selectivity remains challenging. For this case, we here design a hybrid catalyst, synthesized by in situ deposition of Ag crystals on GaN nanobelts, that delivers a tunable H2/CO ratio between 0.5 and 3 under visible light irradiation (λ > 400 nm). The obtained photocatalyst delivers a maximal turnover frequency value of 3.85 h–1 and a corresponding yield rate of 2.12 mmol h–1 g–1 for CO production, while the photocatalytic activity keeps stable during five cycling tests. Additionally, syngas can be detected even at λ > 600 nm. Experiments and mechanistic studies reveal that the existence of Ag crystals not only extends the light absorption region but also promotes the charge transfer efficiency, and thereby leading to a photocatalytic improvement. Accordingly, the present work affords an opportunity for developing an efficient photo-driven system by using solar energy to alleviate CO2 emissions.

Revealing the stability of CuWO4/g-C3N4 nanocomposite for photocatalytic tetracycline degradation from the aqueous environment and DFT analysis

Graphitic carbon nitride (g-C3N4) is an emerging metal-free photocatalyst, however, engineering the photocatalytic efficiency for the effective degradation of hazardous molecules is still challenging. An unstable and low bandgap CuWO4 was composited with g-C3N4 to achieve synergistic benefits of tuning the visible light responsiveness and stability of CuWO4. CuWO4/g-C3N4 nanocomposite exhibited a relatively high visible light absorption region and the bandgap was modified from 2.77 to 2.53 eV evidenced via UV-DRS. Moreover, the fast electron transfer rate was observed with CuWO4/g-C3N4 nanocomposite as confirmed using PL and photocurrent studies. XRD, FT-IR, and HR-TEM analyses signified the formation of CuWO4/g-C3N4 nanocomposite. CuWO4/g-C3N4 nanocomposite showed enhanced photocatalytic degradation of Tetracycline (TC) about ∼7.4 fold greater than pristine g-C3N4 in 120 min. Notably, the OH• and •O2− radicals played a most significant role in photocatalytic TC degradation. Furthermore, the energy band structure, density of state, and Bader charge analyses of these molecules were performed.

Solar energy storage by a microfluidic all-vanadium photoelectrochemical flow cell with self-doped TiO2 photoanode

All-vanadium photoelectrochemical flow cell, which combines the vanadium redox flow battery and the photoelectrochemical flow cell, is a promising technology to store solar energy in reversible redox pairs. The development of a high-performance photoanode is vital to promote the storage of solar energy. In this work, we developed a self-doped TiO2 photoanode and applied it to a microfluidic all-vanadium photoelectrochemical flow cell (μVPFC). The self-doped TiO2 photoanode was simply prepared by annealing the TiO2 photoanode with NaBH4 in the nitrogen atmosphere, by which the self-dopant led to the formation of a disordered layer on the surface and created a mid-band. As a result, the light absorption region was extended and the electron-hole pair separation efficiency was enhanced, promoting the capability of the μVPFC with the self-doped TiO2 photoanode. The superiority of the self-doped TiO2 photoanode was confirmed by its excellent photoelectrochemical performance and vanadium ion conversion rate. The μVPFC with the self-doped TiO2 photoanode yielded an average photocurrent density as high as 0.064 mA·cm−2 in 6-h operation, which was much higher than the reported TiO2 and Ti2O3 photoanodes and presented the improvements by approximately 167% and 60%, respectively. In addition, intensifying the intensity of light and concentration of vanadium ion enabled the performance of the μVPFC with the self-doped TiO2 photoanode to be promoted.

Synthesis of a novel Z-scheme Ag/WO3/g-C3N4 nanophotocatalyst for degradation of oxytetracycline hydrochloride under visible light

In this work, Ag/WO3/g-C3N4 (AWC) nanocomposites were successfully prepared via a hydrothermal method. Oxytetracycline hydrochloride (OTC) was used to evaluate the photocatalytic activity of the photocatalysts under visible light. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra (Raman), scanning electron microscope (SEM), Ultraviolet–visible spectroscopy (UV–vis DRS), photocurrent density (I-t) and electrochemical impedance spectra (EIS). The results showed that WO3 and Ag nanoparticles were coupled with g-C3N4 successfully. Comparing with pure WO3 or g-C3N4, the visible light absorption region of AWC composites was effectively broadened. The photocatalytic performance experiment illustrated that AWC-2 composite had the highest photocatalytic activity, and 97.74% of OTC (10 mg/L) was degraded in 60 min with 0.4 g/L of AWC-2. The radical scavenging experiments indicated that the superoxide radical (•O2−) and hydroxyl radical (•OH) were the most important active species for OTC oxidation. The five cycle photocatalysis experiment further proved that AWC is a stable photocatalyst for degradation of OTC. Finally, the possible degradation mechanism of Z-scheme heterostructure photocatalysis was proposed according to the experimental results.

Synthesis of an ultrathin MnO2 nanosheet-coated Bi2WO6 nanosheet as a heterojunction photocatalyst with enhanced photocatalytic activity

A MnO2/Bi2WO6 heterojunction photocatalyst was synthesized by simple hydrothermal method and characterized systematically. The results showed that ultrathin MnO2 nanosheets are evenly attached on the surface of Bi2WO6 nanosheets to form interfaces between MnO2 and Bi2WO6 and retains 3D flower-like structure of Bi2WO6. The MnO2 addition to Bi2WO6 increases the specific surface area, widens the light absorption region, and changes the electronic properties of Bi and W. Moreover, the defective Mn3+ increases oxygen vacancies and plays a rapid charge transfer role. A good energy band structure is formed in MnO2/Bi2WO6 to facilitate the photogenerated carrier separation. The photocatalytic studies suggest that MnO2/Bi2WO6 shows excellent photocatalytic efficiency and stability for the degradation of NO under light irradiation and inhibition for NO2 generation. MnO2/Bi2WO6 photocatalyst can produce more •OH and •O2− radicals than Bi2WO6, and the electron transfer among Mn ions enhances the removal of NO.

Synthesis of n-Alkoxy Derivatives of Layered Perovskite-Like Niobate HCa2Nb3O10 and Study of Their Photocatalytic Activity for Hydrogen Production from an Aqueous Solution of Methanol

A series of hybrid inorganic–organic niobates HCa2Nb3O10×ROH, containing n-alkoxy groups of primary alcohols (R = Me, Et, Pr, Bu, Hx, and Dc) grafted in the interlayer space, has been studied for the first time in relation to photocatalytic hydrogen generation from a model 1 mol % aqueous solution of methanol under ultraviolet irradiation. Photocatalytic activity was measured both for bare samples and for their composites with Pt nanoparticles as a cocatalyst. The advanced measurement scheme allowed monitoring the volume concentration of a sample in a suspension during the experiment, its pH, and possible exfoliation of layered compounds into nanolayers. In the series of n-alkoxy derivatives, the maximum rate of hydrogen evolution was achieved over a Pt-loaded ethoxy derivative HCa2Nb3O10×EtOH/Pt. Its apparent quantum efficiency of 20.6% in the 220–350 nm range was found not to be caused by changes in the light absorption region or specific surface area upon ethanol grafting. Moreover, the amounts of hydrogen released during the measurements significantly exceeded those of interlayer organic components, indicating that hydrogen is generated from the reaction solution rather than from the hybrid material.

Robust Cr(VI) reduction over hydroxyl modified UiO-66 photocatalyst constructed from mixed ligands: Performances and mechanism insight with or without tartaric acid

Hydroxyl modified UiO-66 ((OH)2-UiO-66-X%, X represents the mass content ratio of introduced 2,5-dihydroxyterephthalic acid) was prepared via a solvothermal reaction between zirconium tetrachloride, benzene-1,4-dicarboxylic acid (H2BDC), as well as 2,5-dihydroxyterephthalic acid (H2BDC-(OH)2). It was found that hydroxyl groups can act as the intramolecular hole scavenger to boost the photo-induced charge carrier separation to enhance Cr(VI) reduction. The photocatalytic Cr(VI) reduction activities of (OH)2-UiO-66-X% were investigated upon the irradiation of low-power ultraviolet LED light. The findings demonstrated that (OH)2-UiO-66-20% with good cyclicity and stability exhibited superior photocatalytic performances to both UiO-66 and (OH)2-UiO-66. The introduction of hydroxyl groups can also extend the light absorption region to longer wavelength in visible range, which provides possibility for displaying photocatalytic activities under sunlight. The effect of small molecule organic acid (SOAs), pH value, and co-existing inorganic ions on photocatalytic performances of (OH)2-UiO-66-20% were investigated. Tartaric acid (TA) as typical SOAs was introduced to the reaction system to further boost the photocatalytic Cr(VI) reduction via acting as hole scavenger, constructing charge-transfer-complex for quick electron transportation, and producing COO·- radicals. This work opened a new opportunity for modified MOFs for boosted elimination activities for environmental pollutants.

Fabrication of novel FeS2 NWs/Ti3C2 cathode for Photo-Electro-Fenton degradation of sulfamethazine

A novel pyrite nanowires (FeS2 NWs)/Ti3C2 composite with 1D-2D hybrid was developed as the cathode for efficient removal of sulfamethazine (SMT) through Photo-Electro-Fenton (PEF) mechanism. FeS2 NWs demonstrated the best PEF performance among different iron sulfide crystalline phases (pyrite, pyrrhotite and mackinawite). The FeS2 NWs/Ti3C2 (FeS2:Ti3C2 = 2:1) cathode exhibited the highest PEF degradation efficiency of 97.6% for SMT (10 mg/L) within 80 min. Diffuse reflection spectra (DRS) indicated the superior light absorption of FeS2 due to the narrow band gap, and Ti3C2 further improved the light utilization of the composite by separating the photogenerated charge carriers and broadening the light absorption region. Photocurrent and electrochemical impedance spectroscopy (EIS) demonstrated the low resistance and rapid charge transfer of FeS2 NWs. Meanwhile, the conductivity of the composite was enhanced by the introduction of Ti3C2, which was ascribed to the promoted electron migration and prolonged carrier lifetime. The FeS2 NWs/Ti3C2 cathode showed excellent recyclability of preserving 92.8% of initial performance after five cycles due to the rapid Fe3+/Fe2+ cycling. Excellent selectivity was also revealed for the FeS2 NWs/Ti3C2 cathode toward two-electron oxygen reduction reaction (ORR) pathway (n = 2.34), ensuring constant H2O2 generation. The radical scavenging experiment also demonstrated that the main oxidant in PEF system was OH. This work paves the way for the novel design and synthesis of highly efficient PEF cathodes.

Facile synthesis of cobalt doped BiOCl ultrathin nanosheets as superior photocatalyst for degradation of carbamazepine under visible light

Herein, novel cobalt-doped bismuth oxychloride ultrathin nanosheets (BiOCl–Co-T) were facilely synthesized by tetrabutylammonium hydroxide (TBAOH) assisted hydrolysis route in water at ambient conditions. Characterizations were performed to investigate the structure, morphology, light absorption ability, electric property, BET surface area and pore structure of the as-prepared samples. The photocatalytic performance was investigated by degrading the persistent contaminant of carbamazepine (CBZ) under visible light irradiation. Results showed that the BiOCl–Co-T displayed enhanced visible-light-driven photocatalytic activity due to the expanded light absorption region and facilitated photogenerated carrier separation. Compared with the degradation efficiencies of 48.4 and 53.8% in BiOCl–Co and BiOCl-T, BiOCl–Co-T exhibited significant improved degradation efficiency of 86.4% within 180 ​min under visible light irradiation. Quenching experiments suggested that holes (h+), superoxide radicals (·O2-), and hydroxyl radicals (·OH) participated in CBZ degradation over BiOCl–Co-T. The obtained result provides a new insight to fabricate visible-light-driven photocatalyst with ultrathin nanosheets shaped structure.

Study of structural, electronic and optical properties of co-doped CeO2 using the density functional theory (DFT) method

The (B, C), (B, H), (B, N), (B, O), (B, P) and (B, S) co-doping effects on structural, electronic and optical properties of CeO2 systems have been studied to determine their potential for photo-catalytic activity using density functional theory and Hubbard U method. Both metallic and nonmetallic co-doping of elements show increase in cell volume and produce local lattice distortion. Due to this co-doping, energy gap between valence and conduction bands becomes narrower than that of pure CeO2, which provides easy way for the transfer of electrons from oxygen 2p orbitals to Ce 4f orbitals assisting in the process for photo-catalysis. Atomic orbitals of similar energy are mixed together except for the atomic s orbital of hydrogen atom. Further, optical absorption peaks for (B, C), (B, H) and ((B, N) co-doped CeO2 systems are found at higher energy range (blue shift) predicting to be better photo-catalytic material. Co-doped CeO2 materials are expected to speed up photoreaction and more electromagnetic waves are allowed to pass through them. Co-doping causes impurity levels to appear in the forbidden energy gap. Extended visible light absorption region has been observed leading to photo-catalytic activity enhancement for the visible light range (~1.5–6.2 eV).

Fabrication of coatings based on strontium-bismuth-silicate photocatalyst for water purification from organic pollutants

Strontium-bismuth containing photocatalytic active coatings on a silicate carrier using sorbite-nitrate pyrolytic synthesis were obtained. The effect of strontium-bismuth molar ratio in the precursor mixture on the phase composition, boundaries of the visible light absorption region and photocatalytic activity of the coatings obtained were studied. The best photocatalytic activity is achieved by coatings obtained from the precursor mixture at Sr:Bi molar ratio of (1:3) and (1:4) in the experiment with a model organic pollutant — methylene blue (MB). The obtained photocatalytically active coatings on silicate carrier (Sr:Bi-1:4) were tested in a water purification unit (WPU) at different rotation speeds. The effective range of rotation of samples without loss of photocatalytic properties at photo-oxidation of MB (15–35 rpm) was established.

Bi2WO6 hollow microspheres with high specific surface area and oxygen vacancies for efficient photocatalysis N2 fixation

In this work, Bi2WO6 hollow microspheres containing oxygen vacancies (OVs-BWO) was synthesized by a solvothermal template-free method. Raman, EPR and XPS spectra provide sufficient evidence for the existence of OVs in the material. Its activity toward photocatalytic nitrogen fixation was evaluated. Experimental results showed that the OVs-BWO with a BET surface area of 80.5 m2·g−1 exhibited the ammonia yield of 106.4 μmol·gcat−1 under simulated sunlight for 2 h, which is ca. 18 times higher than that of equal-area nest-like Bi2WO6 without oxygen vacancies. The enhanced activity is mainly attributed to the metastable electrons within the sub-band (i.e., defect energy level) induced by oxygen vacancies to π anti-bonding orbitals of N2 with a manner of the non-radiative transfer, leading to the activation of nitrogen molecules. The activation and hydrogeneration processes of nitrogen at active site of OVs-BWO were studied by DFT calculation and the possible mechanisms were proposed. The sub-band extends the light absorption region of OVs-BWO to 700 nm. Transient photocurrent response showed that the sub-band electron excitation accelerates the transfer of charges and hinders the electron-hole recombination. It can be perfectly reused five times when air and nitrogen are used as nitrogen sources, thus the OVs-BWO hollow microspheres offer a promising alternative for efficient N2 fixation under ambient conditions.