PdCu alloy anchored defective titania for photocatalytic conversion of carbon dioxide into methane with 100% selectivity

The photoreduction of CO_(2)into CH_(4)with simultaneous high activity and selectivity is a promising strategy to increase energy supply and alleviate global warming.However,the absence of the active sites that is responsible for the adsorption and activation of CO_(2)and the generation of CO and H2via side reactions often lead to poor efficiency and low selectivity of the catalyst.Herein,Cu,Pd,and PdCu metal clusters cocatalyst-anchored defective TiO_(2)nanotubes(Cu/TiO_(2)-SBO,Pd/TiO_(2)-SBO,and Pd1Cu1/TiO_(2)-SBO)were designed via a simple solution impregnation reduction and applied for photocatalytic conversion of CO_(2)to CH_(4).The Pd1Cu1/TiO_(2)-SBO photocatalyst exhibits excellent catalytic performance among the other catalysts for photoreduction of CO_(2)into CH_(4).More interestingly,the product selectivity of CH_(4)reaches up to 100%with a rate of 25μmol g^(-1)h^(-1).In-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)and density functional theory(DFT)simulations indicate that the main reasons for the high selectivity of CH_(4)are attributed to the PdCu alloy and oxygen vacancies,which jointly enhance the photoinduced carrier separation and lower energy barriers of key intermediates.Moreover,due to the tunable d-band center of the Cu site in the PdCu alloy,the generated intermediates can be well prevented from poisoning and promoted to participate in further reactions.Hopefully,the current study will provide insight into the development of new,highly selective photocatalysts for the visible light-catalytic reduction of CO_(2)into CH_(4).

Photocatalytic Performance and Mechanism Study of High Specific Area TiO_(2) Combined with g-C_(3)N_(4)

g-C_(3)N_(4) coupled with high specific area TiO_(2)(HSA-TiO_(2))composite was prepared by a simple solvothermal method,which was easy to operate with low energy consumption.Degradation of methyl orange test results showed that HSA-TiO_(2) effectively improved the photocatalytic activity effectively.Photoelectrochemical test results indicated that the separation of photo-generated carriers and the charge carrier migration speed of TiO_(2) were improved after combination with g-C_(3)N_(4).g-C3N4/HSA-TiO_(2) showed strong photocatalytic ability.The degree of degradation of methyl orange by 6%-g-C_(3)N_(4)/HSA-TiO_(2) could reach up to 92.44%.Furthermore,it revealed good cycle performance.The photocatalytic mechanism of g-C_(3)N_(4)/HSA-TiO_(2) was proposed.

Developing high photocatalytic antibacterial Zn electrodeposited coatings through Schottky junction with Fe3+-doped alkalized g-C_(3)N_(4) photocatalysts

Pure Zn coatings easily lose their protective performance after biofouling because they have no antibacterial effect under visible light.In this study,we fabricate a new antibacterial Zn composite coating using electrodeposition to couple Fe3+-doped alkalized g-C_(3)N_(4)(AKCN-Fe)into an existing Zn coating and show that the AKCN-Fe enhances antibacterial property of the Zn coating under visible light.We attribute this enhancement to the high photocatalytic performance,high loading content,and good dispersion of AKCN-Fe.In addition,the photocatalytic antibacterial mechanism of the composite coating is supported by scavenger experiments and electron paramagnetic resonance(EPR)measurements,suggesting that superoxide(·O_(2)^(-))and hydroxyl radical(·OH)play main and secondary roles,respectively.

Facile synthesis of Ag_2O-TiO_2/sepiolite composites with enhanced visible-light photocatalytic properties

Ag2O-TiO 2/sepiolite heterostructure composites were synthesized by a simple two-step method at low temperatures（100–450 °C）. Acid red G aqueous solution and gaseous formaldehyde were chosen as model organic pollutants to evaluate the photocatalytic performance of the as-prepared composites. The results showed that the Ag2O-TiO 2/sepiolite exhibited enhanced photocatalytic activity over pure Ag2O-TiO 2,TiO 2/sepiolite,and Ag2O/sepiolite under visible-light irradiation（λ 420 nm）. The excellent photocatalytic efficiency of these composites can be ascribed to the synergistic effect between the heterojunction and the porous structure of the clay layers,which induced high adsorption and efficient charge separation. In addition,the active species involved in the degradation reaction have been investigated by photoluminescence spectroscopy and quenching experiments. A possible photocatalytic degradation mechanism of acid red G dye by the Ag2O-TiO 2/sepiolite composite is also discussed.

ZIF-8 modified by isocyanate as a photocatalytic antibacterial agent

Zeolite imidazole skeleton(ZIF-8)is a promising option for self-cleaning of building exterior walls due to its large specific surface area,high antibacterial activity and low biotoxicity.However,it suffers from low antibacterial efficiency and yield under visible light irradiation.To address the issues,we developed the photocatalytic materials T-ZIF-8-TDI(thermally treated-ZIF-8-toluene 2,4-diisocyanate)by modifying ZIF-8 with thermal oxygen sensitization and chemical bonding.The results show that the yield of T-ZIF-8-TDI photocatalytic antibacterial agent is increased to 11.5 times of that of T-ZIF-8,while maintaining the crystal structure of T-ZIF-8 and thermal stability up to 60℃.Furthermore,T-ZIF-8-TDI exhibits extended optical response range to the nearinfrared region,significantly narrowed band gap,improved photogenerated elec tron-hole separation efficiency,reduced recombination rate,and excellent photocatalytic performance.When the concentration of antibacterial agent is 600 mg·L^(-1),the antibacterial rate of Escherichia coli(E.coli)reaches 99.99%irradiated by visible light for30 min,and when the concentration of antibacterial agent is 200 mg·L^(-1),the antibacterial rate of Staphylococcus aureus(S.aureus)reaches 99.99%irradiated by visible light for 25 min.We also analyzed the reasons in detail from the aspects of bacterial species and antibacterial mechanism,and proposed the antibacterial mechanism of·O_(2)^(-)and h^(+)as the main active species.These findings suggest that T-ZIF-8-TDI photocatalytic antibacterial agent has potential for use in self-cleaning of building exterior walls.

Combination Mechanism and Enhanced Visible-Light Photocatalytic Activity and Stability of CdS/g-C3N4 Heterojunctions

In this study, CdS/g-C3N4 （CSCN） heterojunctions were in situ fabricated with a large amount of CdS nanoparticles anchored on g-C3N4 nanosheets, A wet chemical method was developed for the first time to determine the actual content of CdS in CSCN composites. X-ray diffraction （XRD）, Fourier transform infrared spectra （FFIR）, high-resolution transmission electron microscopy （HRTEM） and UV-vis diffuse reflectance spectra （DRS） were employed to characterize the composition, structure and optical prop- erty of CSCN composites. Based on the is0electric point （liP） analysis of g-C3N4, a conclusion was obtained on the combination mechanism between CdS nanoparticles and g-C3N4 nanosheets. The photocatalytic activity of CSCN composites was much better than those of individual CdS and g-C3N4 for the degrada- tion of azo dye Methyl Orange （MO） by 40 min adsorption in the dark followed by 15 min photocatalysis under visible light irradiation. After 5 cycles, CSCN composites still maintained high reactive activity with the MO degradation efficiency of 93.8%, exhibiting good photocatalytic stability. The Cd2~ concentration dissolved in the supernatant detected by atomic absorption spectroscopy （AAS） of CSCN composites was lower than that of pure CdS, implying that the photocorrosion of CdS could be suppressed via the combination with g-C3N4. Photoluminescence emission spectra （PL） results clearly revealed that the recombination of photogenerated electron-hole pairs in CSCN composites was effectively inhibited due to the formation of heterojunctions. Based on the band alignments of g-C3N4 and CdS, the possible photocatalvtic mechnism was discussed.

Wheel-shaped icosanuclear Cu-containing polyoxometalate catalyst: Mechanistic and stability studies on light-driven hydrogen generation

In this paper,we report the synthesis and characterization of a wheel-shaped icosanuclear Cu-containing polyoxometalate(POM),K_(12)Li_(13)[Cu_(2)0Cl(OH)_(24)(H_(2)O)_(12)(P_(8)W_(48)O_(184))]·22H_(2)O(K_(12)Li_(13)-Cu_(2)0P_(8)W_(48)).The resulting cation-exchanged tetrabutylammonium salt of the polyoxoanion Cu_(2)0P_(8)W_(48)(TBA-Cu_(2)0P_(8)W_(48))exhibits high efficiency for visible-light-driven H_(2) production in the presence of an[Ir(ppy)2(dtbbpy)][PF_(6)]photosensitizer and a triethanolamine electron donor.Under optimal conditions,the turnover number for H_(2) production reaches~2892 after 5 h of photocatalysis and thereafter continuously increases to~13400 in a long-term 120 h reaction,representing the best performance among all reported transition-metal-substituted POM catalysts.Mechanistic studies confirm the existence of reductive and oxidative quenching processes,of which the reductive quenching pathway is dominant.Various stability tests demonstrate that the TBA-Cu_(2)0P_(8)W_(48) catalyst slowly dissociates Cu ions under turnover conditions;however,both the starting TBA-Cu_(2)0P_(8)W_(48) and its molecular decomposition products are dominant active species for efficient and long-term H_(2) production.

TiO2/g-C3N4 heterojunctions： In situ fabrication mechanism and enhanced photocatalytic activity

In situ fabrication of TiO21g-C3N4 （TCN） heterojunctions was achieved by a modified sol-gel method. TG analysis was employed to determine the content of Ti02 in TCN composites. XRD, FTIR, TEM and HRTEM were used to analyze the phase composition, functional groups, morphology and microstructure of as-obtained pro- ducts, respectively. Based on the measurement of surface Zeta potential of g-C3N4, a possible mechanism on in situ fabrication of TCN heterojunctions was concluded. The control experiments indicated that TCN heterojunctlons exhibited better photocatalytic performance than either Ti02 or g-C3N4, suggesting that the enchanced photocatalytic activity could be realized by TCN heterojunctionso Then, the evaluation of parameters affecting the photocatalytic performance of TCN heterojunctions was investigated. Even after five cycles, TCN heterojunctions still maintained high photocatalytic activity, exhibiting the good photocatalytic stability. UV-vis absorption spectra showed that almost all MB molecules were decomposed in the photocatalytic process. Finally, the possible mechanism on enhanced photocatalytic performance of TCN heterojunctions was discussed.

Synthesis of core-shell nanostructured SiO_(2)/TiO_(2)photocatalysts via atomic layer deposition in a fluidized bed with central tube

Fluidized bed atomic layer deposition is an efficient technique for particle coating with precise control over the film thickness and uniformity at the sub-nanoscale.In this study,a fluidized bed with a central tube is designed,where the central tube has two roles:improve fluidization and deliver precursors separately.The synthesis of core-shell structured SiO_(2)/TiO_(2)nanoparticle catalysts for photodegradation of tetracycline hydrochloride(TC)is carried out using TiCl_(4)and H_(2)O as precursors at 180℃under atmospheric pressure.Under the combination of vibration and central tube,the segregation of agglomerate size along the bed height is weakened,and the prepared SiO_(2)/TiO_(2)nanoparticles show excellent photocatalytic degradation performance:the degradation efficiency on TC is 96%under 300 W xenon lamp irradiation for 60 min.The mechanism of enhanced photocatalytic activity is due to the Ti-O-Si bonds generated at the interface,which increase the ability to absorb sunlight and accelerate the separation of holes and electrons.

Recent progress for hydrogen production by photocatalytic natural or simulated seawater splitting

Solar energy is an inexhaustible renewable energy source.Among the various methods for solar energy conversion,photocatalytic hydrogen(H2)production is considered as one of the most promising ways.Since Fujishima pioneered this field in 1972,photocatalytic water splitting to produce H2 has received widespread attention.Up to now,abundant semiconductor materials have been explored as photocatalysts for pure water splitting to produce H2.However,photocatalytic seawater splitting is more in line with the concept of sustainable development,which can greatly alleviate the problem of limited freshwater resource.At present,only few studies have focused on the process of H2 production by photocatalytic seawater splitting due to the complex composition of seawater and lack of suitable photocatalysts.In this review,we outline the most recent advances in photocatalytic seawater splitting.In particular,we introduce the H2 production photocatalysts,underlying mechanism of ions in seawater on photocatalytic seawater splitting,current challenges and future potential advances for this exciting field.

Ag@ Bi2WO6 Composites with High Visible-Light-Driven Photocatalytic Activities Prepared in UV Light Irradiation

Bi2WO6 microstructures were synthesized through hydrothermal process and Ag@Bi2WO6 composites were synthesized by simple UV light irradiation for 5 rain using Bi2WO6 and AgNO3 as raw materials. Ag@BizWO6 composites were characterized by X-ray powder diffraction （XRD）, field-emission scanning electron microscopy （FE-SEM）, and UV-Vis absorption spectrum （UV-Vis）. Few Ag deposited on the Bi2WO6 leads to an increase in photocatalytic activity, which clearly indicates that the recombination of photogenerated charge carrier between the hybrid orbital of Bi6s and O2p （valence band） to the empty W5d orbital is inhibited greatly in the Ag@Bi2WO6 composite. In addition, a few H2O2 will greatly enhance photocatalytic activity of Ag@BizWO6, and the proper reason is discussed.

CdTe QDs@SiO_(2) composite material for efficient photocatalytic degradation of tetracycline composites

In the contemporary context,tetracycline is widely utilized as a prevalent antibiotic in various facets of life.However,the excessive use of antibiotics has caused visible environmental consequences.Henceforth,the scientific community has increasingly focused on developing catalysts that exhibit exceptional efficacy in the proficient degradation of tetracycline.In this study,a novel nanomaterial was developed to encapsulate Cd Te quantum dots(QDs)with a SiO_(2)shell.The distinct synthesis approach generated a composite material that showed heterogeneity and considerably increased the contact area with contaminants.Consequently,the transfer of photoelectron to the SiO_(2)spheres was significantly improved,leading to a more efficient separation during the catalytic process.The study investigated how different factors,such as the loading of the catalyst,the initial concentration of tetracycline,p H levels,and the wight ratio of Cd Te QDs(SiO_(2)+Cd Te QDs)affected the effectiveness of photocatalytic tetracycline degradation.The findings indicated that the optimal degradation efficiency was observed at a catalyst concentration of 0.25 g/L and a solution p H of 9,leading to an impressive degradation rate of 96%within a mere 2 h timeframe.

Fabricating Fe3O4-schwertmannite as a Z-scheme photocatalyst with excellent photocatalysis-Fenton reaction and recyclability

Here we reported an effective method to solve the rate-limiting steps, such as the reduction of Fe^(3+) to Fe^(2+) and an invalid decomposition of H2O2 in a conventional Fenton-like reaction. A magnetic heterogeneous photocatalyst, Fe3O4-schwertmannite(Fe3O4-sch) was successfully developed by adding Fe3O4 in the formation process of schwertmannite. Fe3O4-sch shows excellent electrons transfer ability and high utilization efficiency of H2O2(98.5%). The catalytic activity of Fe3O4-sch was studied through the degradation of phenol in the heterogeneous photo-Fenton process. Phenol degradation at a wide pH(3-9) was up to 98% within 6 min under visible light illumination with the Fe3O4-sch as heterogeneous Fenton catalyst, which was higher than that using pure schwertmannite or Fe3O4. The excellent photocatalytic performance of Fe3O4-sch is ascribed to the effective recycling between ≡Fe^(3+) and ≡Fe^(2+) by the photo-generated electron, and also profit from the formation of the "Z-Scheme" system. According to the relevant data, photocatalytic mechanism of Fe3O4-sch for degrading phenol was proposed. This study not only provides an efficient way of enhancing heterogeneous Fenton reaction, but also gives potential application for iron oxyhydroxysulfate mineral.

Review of the progress in preparing nano TiO_2: An important environmental engineering material

TiO2 nanomaterial is promising with its high potential and outstanding performance in photocatalytic environmental applications, such as CO2 conversion, water treatment, and air quality control. For many of these applications, the particle size, crystal structure and phase, porosity, and surface area influence the activity of TiO2 dramatically. TiO2 nanomaterials with special structures and morphologies, such as nanospheres, nanowires, nanotubes, nanorods, and nanoflowers are thus synthesized due to their desired characteristics. With an emphasis on the different morphologies of TiO2 and the influence factors in the synthesis, this review summarizes fourteen TiO2 preparation methods, such as the sol-gel method, solvothermal method, and reverse micelle method. The TiO2 formation mechanisms, the advantages and disadvantages of the preparation methods, and the photocatalytic environmental application examples are proposed as well.

Carbon dots-based nanocomposites for heterogeneous photocatalysis

Carbon dots(CDs),as a class of promising and multifunctional carbon nanomaterials,have become a research hotspot in the field of photocatalysis owning to strong absorption of visible light,favorable photoelectric properties,and tunable energy-level configuration.Although numerous efforts have been made to improve photocatalytic performance by combining CDs with other semiconductors in recent years,the summary of enhancement mechanisms for this emerging technology is few reported.Fully understanding the synergistic effect of CDs and nanomaterials in photocatalytic applications is extremely important for the further development of photocatalysis in the future.Here,the photocatalytic mechanism of carbon dots/nanomaterial system is discussed.Four typical carbon dots-synergistic enhancement effects are highlighted,namely,energy band regulation,local electric construction,active site engineering,and multiple carrier activation.Second,the recent progress of carbon dots-based nanocomposites in efficient solar energy conversion is reviewed and examples are given.Finally,the future research development direction and challenges are emphasized on this basis.