太阳能光伏光热/催化净化复合技术的研究进展

太阳能光伏光热综合利用系统(PV/T)可产生电能和热能,综合效率大幅提升,但仍存在功能有限、全光谱利用率不高、对回收热能利用形式单一等问题。针对当前PV/T存在的问题,提出太阳能光伏光热/催化净化复合技术的新概念、新系统和新功能。该复合技术实现发电、采暖和净化等多样化功能,并开发了多种太阳能光伏光热/净化建筑一体化系统,不仅进一步提高了系统的综合利用效率、增强了功能性,且提升了室内热环境和空气品质。该文介绍了作者近年来的研究,包括光/热催化型Trombe墙系统、光/热催化型光伏光热复合墙系统、光/热催化型光伏通风窗系统和光伏光热/热除菌杀毒系统,拓展了太阳能光伏光热建筑一体化系统的研究和应用,为实现太阳能在建筑上的高效多功能利用以及营造健康舒适的室内环境提供新方法。

Regulating crystal phase of TiO_(2) to enhance catalytic activity of Ni/TiO_(2) for solar-driven dry reforming of methane

Ni/TiO_(2) catalyst is widely employed for photo-driven DRM reaction while the influence of crystal structure of TiO_(2) remains unclear.In this work,the rutile/anatase ratio in supports was successfully controlled by varying the calcination temperature of anatase-TiO_(2).Structural characterizations revealed that a distinct TiO_(x) coating on the Ni nanoparticles(NPs)was evident for Ni/TiO_(2)-700 catalyst due to strong metal-support interaction.It is observed that the TiOx overlayer gradually disappeared as the ratio of rutile/anatase increased,thereby enhancing the exposure of Ni active sites.The exposed Ni sites enhanced visible light absorption and boosted the dissociation capability of CH4,which led to the much elevated catalytic activity for Ni/TiO_(2)-950 in which rutile dominated.Therefore,the catalytic activity of solar-driven DRM reaction was significantly influenced by the rutile/anatase ratio.Ni/TiO_(2)-950,characterized by a predominant rutile phase,exhibited the highest DRM reactivity,with remarkable H_(2) and CO production rates reaching as high as 87.4 and 220.2 mmol/(g·h),respectively.These rates were approximately 257 and 130 times higher,respectively,compared to those obtained on Ni/TiO_(2)-700 with anatase.This study suggests that the optimization of crystal structure of TiO_(2) support can effectively enhance the performance of photothermal DRM reaction.

锰基氧化物催化降解VOCs的研究进展

挥发性有机化合物(VOCs)是空气污染的主要来源之一,因其对环境和人体健康的严重威胁而受到广泛关注。催化氧化已被证明是一种高效的降解VOCs技术。而作为环境友好且低成本的材料,锰基氧化物成为热催化或光/热催化中降解VOCs最具竞争力和前景的候选材料。本文总结了近年来各种锰基氧化物催化剂(单一锰基氧化物、锰基复合氧化物、表面改性的锰基氧化物以及锰基整体催化剂)的研究进展。最后,提出了锰基氧化物催化氧化VOCs存在的问题及对未来研究进行展望。

Fabrication of a monoclinic/hexagonal junction in WO_3 and its enhanced photocatalytic degradation of rhodamine B

A series of WO3 samples with different crystalline phases were prepared by the thermal decomposition method from ammonium tungstate hydrate.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,high-resolution transmission electron microscopy（HRTEM）,X-ray photoelectron spectroscopy,and N2 adsorption-desorption were used to characterize the crystalline phase,morphology,particle size,chemical composition,and surface area of the WO3 samples.The formation of hexagonal（h-WO3） and monoclinic（m-WO3） crystal structures of WO3 at different temperatures or different times was confirmed by XRD.m-WO3 is formed at 600 ℃,while m-WO3 starts to transform into h-WO3 at 800℃.However,h-WO3,which forms at 800℃,may transform into m-WO3 by increasing the calcination temperature to 1000℃.SEM results indicate that m-WO3 particles exhibit a bulky shape with heavy aggregates,while h-WO3 particles exhibit a rod-like shape.Moreover,m-WO3 crystals are sporadically patched on the surface of the h-WO3 rod-like particles,resulting in the exposure of both m-WO3 and h-WO3 on the surface.It is observed that the monoclinic phase（m-WO3）/hexagonal phase（h-WO3） junction was fabricated by tuning the calcination temperature and calcination time.The relative ratios between m-WO3 and h-WO3 in the phase junction can readily be tailored by control of the calcination time.The photocatalytic activities of WO3 with different crystalline phases were evaluated by the photocatalytic degradation of rhodamine B as a model pollutant.A higher photocatalytic activity was observed in the WO3 sample with the m-WO3/h-WO3junction as compared with the sample with only m-WO3.The improvement of photocatalytic activity can be attributed to the reduction of the electron-hole recombination rate owing to the formation of the phase junction,whose presence has been confirmed by HRTEM and photoluminescence spectra.

Enhanced photocatalytic properties of hierarchical nanostructured TiO_2 spheres synthesized with titanium powders

Using Ti powder as reagent, TiO 2 nanoneedle/nanoribbon spheres were prepared via hydrothermal method in NaOH solution. The samples were characterized by field emission scanning electron microscopy （FESEM）, transmission electron microscopy （TEM） with selected area electron diffraction （SAED）, X-ray diffraction （XRD）, and UV-visible light absorption spectrum. The results indicate that the growth orientations of the crystals are influenced by the hydrothermal temperature and NaOH concentration. The diameter of the nanoneedle spheres and nanoribbon spheres （40 50 μm） are almost the same as that of Ti powders. TiO 2 nanoneedle/nanoribbon sphere powders are anatase after heat treatment at 450 °C for 1 h. Furthermore, methyl orange was used as a target molecule to estimate the photocatalytic activity of the specimens. Under the same testing conditions, the photocatalytic activities of the products decrease in the following order： TiO 2 nanoneedle sphere, TiO 2 nanoribbon sphere and P25.

Mesh-Like Bi2MoO6 with Enhanced and Stable Visible Light Photocatalytic Activity

Mesh-like Bi2MoO6 product was successfully synthesized by a hydrothermal method without using any surfactant or template. The pH value played an important role in the formation of this morphology. The as-prepared mesh-like Bi2MoO6 sample exhibited excellent visible-light-driven photocatalytic e ciency. The photocatalytic activity of the mesh-like Bi2MoO6 sample was much higher than that of bulk Bi2MoO6 sample prepared by solid-state reac-tion. Di erence in the photocatalytic activities of the mesh-like Bi2MoO6 sample and bulk Bi2MoO6 sample was further investigated.

Recent advances in VOCs and CO removal via photothermal synergistic catalysis

Currently,air pollution is being exacerbated by rapid social,economic,and industrial development.Major air pollutants include volatile organic compounds(VOCs)and CO.Photocatalytic and thermocatalytic technology can be used to convert VOCs and CO into harmless gases effectively.Recently,photothermal synergistic catalysis has aroused much attention because of its higher performance than those of individual photocatalytic and thermocatalytic processes.There have been many reviews on separate photocatalysts and thermocatalysts for the treatment of VOCs and CO,but few reviews have focused on photothermal synergistic catalysis.In this minireview,we concentrate on recent progress into photothermal synergistic catalysis for the efficient removal of VOCs and CO.The treatment of typical VOCs(such as benzene,toluene,ethanol,formaldehyde,acetone,propylene,and propane)and CO are summarized and analyzed.Furthermore,we discuss the use of conventional reactor technology,such as fixed‐bed quartz reactors,for VOCs and CO removal.We also discuss the mechanism of the photothermal synergistic catalytic removal of VOCs and CO.Finally,we present perspectives for the photothermal synergistic catalytic removal of VOCs and CO.

Visible light-enhanced photothermal CO2 hydrogenation over Pt/Al2O3 catalyst

Light illumination has been widely used to promote activity and selectivity of traditional thermal catalysts. Nevertheless, the role of light irradiation during catalytic reactions is not well understood. In this work, Pt/Al2 O3 prepared by wet impregnation was used for photothermal CO2 hydrogenation, and it showed a photothermal effect. Hence, operando diffuse reflectance infrared Fourier-transform spectroscopy and density functional theory calculations were conducted on Pt/Al2 O3 to gain insights into the reaction mechanism. The results indicated that CO desorption from Pt sites including step sites(Ptstep) or/and terrace site(Ptterrace) is an important step during CO2 hydrogenation to free the active Pt sites. Notably, visible light illumination and temperature affected the CO desorption in different ways. The calculated adsorption energy of CO on Ptstep and Ptterrace sites was-1.24 and-1.43 e V, respectively. Hence, CO is more strongly bound to the Ptstep sites. During heating in the dark, CO preferentially desorbs from the Ptterrace site. However, the additional light irradiation facilitates transfer of CO from the Ptstep to Ptterrace sites and its subsequent desorption from the Ptterrace sites, thus promoting the CO2 hydrogenation.

Hydrothermal synthesis of monodisperse Zn_(x)Cd_(1-x)S spheres and their photocatalytic properties

Monodisperse ZnxCd1-xS spheres were successfully fabricated with a high yield by a facile hydrothermal route.The as-prepared samples were characterized by X-ray diffractometry,scanning electron microscopy and UV-vis diffusion reflectance spectroscopy.The results indicate that all the prepared samples have the same hexagonal wurtzite phase and exhibit good size uniformity and regularity.Degradation of rhodamine-B（RhB） was used to evaluate the photocatalytic activities of ZnxCd1-xS samples.Zn0.4Cd0.6S possessed the best photocatalytic activity and exhibited high stability during the reaction.

Influence of Ag on photocatalytic performance of Ag/ZnO nanosheet photocatalysts

Ag/ZnO nanosheet composites were prepared by zinc nitrate, sodium hydroxide and silver nitrate via a simple hydrothermal method. The crystal structure, morphology, optical property and photocatalytic performance were studied by means of XRD, SEM, HRTEM, XPS, and PL methods. It is found that both the pure ZnO and composite Ag/ZnO samples have the same morphology of nanosheet. The interaction of spherical Ag particles with ZnO matrix in the Ag/ZnO sample leads to an increase in photocatalytic efficiency for the possible increase of concentration of surface hydroxyl and the photo-induced electrons and holes. The addition of Ag can reduce the recombination rate of photo-generated carriers and the sample with addition of 3 at% Ag to ZnO exhibits the best photocatalytic activity with the degradation rate up to 95% within 15 min.

Highly efficient UV-visible-infrared photothermocatalytic removal of ethyl acetate over a nanocomposite of CeO_(2) and Ce-doped manganese oxide

A unique nanocomposite of CeO_(2)nanoparticles and Ce-doped manganese oxide nanofibers having a crystalline cryptomelane-type octahedral molecular sieve(KMn_(8)O_(16)·nH_(2)O,abbreviated as OMS-2)structure(denoted CeO_(2)-CeOMS-2)was prepared by the reaction of Ce(NO_(3))3 and KMnO_(4)at 90°C.CeO_(2)-CeOMS-2 shows extremely high photothermocatalytic activity,very low selectivity for acetaldehyde(an unfavorable byproduct),and excellent durability for ethyl acetate removal under UV-visible-infrared(UV-vis-IR)irradiation.In striking contrast,pure CeO_(2),pure OMS-2,and TiO_(2)(P25)showed much lower photothermocatalytic activities and higher selectivities for acetaldehyde.The CO_(2)production rate within the first five minutes(r CO2)of reaction with CeO_(2)-CeOMS-2 was as high as 1102.5μmol g-1 min-1,which is 137,17,and 30-times higher than those of pure CeO_(2),pure OMS-2,and TiO_(2)(P25),respectively.CeO_(2)-CeOMS-2 also shows good photothermocatalytic activity under vis-IR(λ>420 or 560 nm)irradiation.Further,even under vis-IR(λ>830 nm)irradiation,efficient photothermocatalytic activity was achieved.In addition,the catalytic activity of CeO_(2)-CeOMS-2 is far superior to those of pure CeO_(2)and OMS-2,which is attributed to the fact that Ce doping significantly improves the lattice oxygen activity of OMS-2.The high photothermocatalytic activity of CeO_(2)-CeOMS-2 arises from the synergy between the photocatalytic effect of the CeO_(2)nanoparticles and light-driven thermocatalysis of the Ce-doped OMS-2.The novel photoactivation of Ce-doped OMS-2,which is unlike that of conventional photocatalysis on semiconductor photocatalysts,further promotes the catalytic activity because the surface oxygen activity of Ce-doped OMS-2 is promoted upon UV-vis-IR or vis-IR(λ>560 nm)irradiation.

Synergetic photocatalytic and thermocatalytic reforming of methanol for hydrogen production based on Pt@TiO_(2) catalyst

In order to efficiently produce H_(2),conventional methanol‐water thermocatalytic(TC)reforming requires a very high temperature due to high Gibbs free energy,while the energy conversion efficiency of methanol‐water photocatalytic(PC)reforming is far from satisfaction because of the kinetic limitation.To address these issues,herein,we incorporate PC and TC processes together in a specially designed reactor and realize simultaneous photocatalytic/thermocatalytic(PC‐TC)reforming of methanol in an aqueous phase.Such a design facilitates the synergetic effect of the PC and TC process for H_(2) production due to a lower energy barrier and faster reaction kinetics.The methanol‐water reforming based on the optimized 0.05%Pt@TiO_(2) catalyst delivers an outstanding H_(2) production rate in the PC‐TC process(5.66μmol H_(2)·g^(‒1) catalyst·s^(‒1)),which is about 3 and 7 times than those of the TC process(1.89μmol H_(2)·g^(‒1) catalyst·s^(‒1))and the PC process(0.80μmol H_(2)·g^(‒1) catalyst·s^(‒1)),respectively.Isotope tracer experiments,active intermediate trapping experiments,and theoretical calculations demonstrate that the photo‐generated holes and hydroxyl radicals could enhance the methanol dehydrogenation,water molecule splitting,and water‐gas shift reaction,while high temperature accelerates reaction kinetics.The proposed PC‐TC reforming of methanol for hydrogen production can be a promising technology to solve the energy and environmental issue in the closed‐loop hydrogen economy in the near future.

Thermal coupled photoconductivity as a tool to understand the photothermal catalytic reduction of CO2

Photocatalysis shows great promise in the field of solar energy conversion.One of the reasons for this is because it promotes the development of multi-field-coupled catalysis.In order to explore the principles of multi-field-coupled catalytic reactions,an in situ multi-field-coupled characterization technique is required.In this study,we obtained hydrogenated ST-01 TiO2 and observed enhanced catalytic activity by thermal coupled photocatalysis.In situ photoconductivity was employed to understand the activity enhancement.The effects of the reaction temperature,reaction atmosphere,and oxygen vacancy(Ov)on the photoconductivity of TiO2 were studied.After coupling thermal into photoconductivity measurement,highly active Ov-TiO2 displayed rapid decay of photoconductivity in a CO2 atmosphere and slow decay of photoconductivity in a N2 atmosphere.These phenomena revealed that photothermal coupling assisted the detrapping of electrons at the Ov surface and promoted electron transfer to CO2,which clearly explained the high photothermal catalytic activity of Ov-TiO2.This study demonstrated that photoconductivity is a useful tool to help understand photothermal catalytic phenomena.

Synthesis of Bi_2S_3 microsphere and its efficient photocatalytic activity under visible-light irradiation

A novel Bi2S3 microsphere was fabricated through one-pot urea-assisted solvothermal method.The synthesized Bi2S3 microsphere was characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),Fourier transformed infrared spectroscopy(FT-IR)and thermal gravimetric analysis and differential thermal analysis(DTA-TG).Subsequently,the photocatalytic performances of Bi2S3 microsphere were evaluated by photocatalytic degradation of methyl orange(MO)simulation solution under visible-light irradiation.The results show that,Bi2S3 microsphere could be used as a potential cost-efficient catalysis for eliminating of methyl orange from aqueous solutions,whose degradation rate could reach 91.07%within 180 min.Besides,a tentative photocatalytic reaction mechanism was discussed according to the energy band position.Therefore,this work indicated a simplistic approach for the fabrication of visible-light responsive Bi2S3 microsphere photocatalyst,which can be used as a valuable candidate in solar energy conversion and environment pollution treatment.

High-humidity tolerance of porous TiO2(B)microspheres in photo thermal catalytic removal of NOx

Semiconductor oxides are widely used to achieve photocatalytic removal of NOx(NO and NO2) species. These materials also exhibit enhanced oxidation ability in thermally assisted photocatalysis;however, many of them tend to be deactivated at high relative humidity(RH) levels. In the case of the benchmark P25 TiO2 photocatalyst, we observe a significant decrease in non-NO2 selectivity from 95.02% to 58.33% when RH increases from 20% to 80%. Interestingly, the porous TiO2(B) microspheres synthesized in this work exhibit 99% selectivity at 20% RH;the selectivity remains as high as 96.18% at 80% RH. The high humidity tolerance of the TiO2(B) sample can be ascribed to its strong water desorption capacity and easy O2 adsorption at elevated temperatures, which reflects the fact that the superoxide radical is the main active species for the deep oxidation of NOx. This work may inspire the design of efficient photothermal catalysts with application in NOx removal in hot and humid environments.

Engineering graphitic carbon nitride with expanded interlayer distance for boosting photocatalytic hydrogen evolution

Regulating interlayer distance is a crucial factor in the development of two‐dimensional(2D)nanomaterials.A 2D metal‐free photocatalyst,such as graphitic carbon nitride(g‐C3N4),exhibits morphology‐and microstructure‐dependent photocatalytic activity.Herein,we report a straightforward and facile route for the preparation of unique lamellar g‐C3N4,by co‐firing melamine and ammonium chloride via microwave‐assisted heating.Through the decomposition of NH4Cl,the evaporation of NH3 gas can effectively overcome van der Waals forces,expanding the interlayer distance of g‐C3N4,thereby creating a lamellar structure consisting of nanosheets.Compared with bulk g‐C3N4,the NH3‐derived lamellar g‐C3N4 exhibits a larger specific surface area and enhanced optical absorption capability,which increase photocatalytic hydrogen production because of the highly active structure,excellent utilization efficiency of photon energy,and low recombination efficiency of photogenerated charge carriers.This study provides a simple strategy for the regulation of the g‐C3N4 microstructure toward highly efficient photocatalytic applications.

Pyroelectricity effect on photoactivating palladium nanoparticles in PbTiO3 for Suzuki coupling reaction

Combining microwave radiation with photocatalytic systems is a promising method to inhibit photogenerated electron-hole recombination and enhance the photocatalytic reaction performance. In this study, we have designed Pd/Pb TiO3 catalysts that can use both microwave fields and photocatalysis. Benefiting from the synergistic effect of microwave field and UV light, the Pb TiO3 crystals convert thermal energy into electrical energy via the pyroelectricity effect, generating positive and negative charges(q+ and q-), while Pd nanoparticles significantly improve the quantum efficiency of the photocatalytic process. The composite catalyst significantly enhances the reaction rate and selectivity of the model Suzuki coupling reaction performed with bromobenzene. Microwave fields can directly act on chemical systems, promoting or changing various chemical reactions in unique ways.

Synergistic photo-thermal catalytic NO purification of MnO_x/g-C_3N_4:Enhanced performance and reaction mechanism

Both MnOx and g‐C3N4 have been proved to be active in the catalytic oxidation of NO,and their individual mechanisms for catalytic NO conversion have also been investigated.However,the mechanism of photo‐thermal catalysis of the MnOx/g‐C3N4 composite remains unresolved.In this paper,MnOx/g‐C3N4 catalysts with different molar ratios were synthesized by the precipitation approach at room temperature.The as‐prepared catalysts exhibit excellent synergistic photo‐thermal catalytic performance towards the purification of NO in air.The MnOx/g‐C3N4 catalysts contain MnOx with different valence states on the surface of g‐C3N4.The thermal catalytic reaction for NO oxidation on MnOx and the photo‐thermal catalytic reaction on 1:5 MnOx/g‐C3N4 were investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS).The results show that light exerted a weak effect on NO oxidation over MnOx,and it exerted a positive synergistic effect on NO conversion over 1:5 MnOx/g‐C3N4.A synergistic photo‐thermal catalytic cycle of NO oxidation on MnOx/g‐C3N4 is proposed.Specifically,photo‐generated electrons(e?)are transferred to MnOx and participate in the synergistic photo‐thermal reduction cycle(Mn4+→Mn3+→Mn2+).The reverse cycle(Mn2+→Mn3+→Mn4+)can regenerate the active oxygen vacancy sites and inject electrons into the g‐C3N4 hole(h+).The active oxygen(O?)was generated in the redox cycles among manganese species(Mn4+/Mn3+/Mn2+)and could oxidize the intermediates(NOH and N2O2?)to final products(NO2?and NO3?).This paper can provide insightful guidance for the development of better catalysts for NOx purification.

Hydrothermal synthesis and enhanced photocatalytic activity of hierarchical flower-like Fe-doped BiVO_4

Fe-doped BiVO4with hierarchical flower-like structure was prepared via a hydrothermal method using sodium dodecylbenzene sulfonate(SDBS)as structure directing agent.X-ray diffraction(XRD),scanning electron microscope(SEM),transmissionelectron microscope(TEM),high resolution transmission electron microscope(HRTEM),X-ray photoelectron spectroscopy(XPS)and UV-Vis were applied for characterization of the as-prepared samples.The formation mechanism of flower-like structure wasproposed based on the evolution of morphology as a function of hydrothermal time.Fe-doped into substitutional sites of BiVO4effectively improved the migration and separation of photogenerated carrier and enhanced the utilization of visible light.Flower-likeFe-doped BiVO4showed much higher visible-light-driven photocatalytic efficiency for degradation of methyl blue compared withthe pristine BiVO4.And the sample with a Fe/Bi mole ratio of2.5%showed the highest photocatalytic efficiency.

C-I codoped porous g-C_3N_4 for superior photocatalytic hydrogen evolution

Porous C‐I codoped carbon nitride materials were synthesized by in‐situ codoping with iodized ionic liquid followed by post‐thermal treatment in air.The effects of doping content of C‐I codoping with different amounts of ionic liquid on the structural,optical and photocatalytic properties of the samples were investigated.Characterization results show that more compact interlayer sacking can be achieved by post‐thermal treatment.Combined with C‐I codoping by insertion of ionic liquids,much enlarged surface area but optimized sp2 conjugated heterocyclic structure can be found in the catalysts.Optical and energy band analysis results evidence that the light absorptions especially in visible light region are significantly improved.Although the band gap of porous C‐I codoped samples enlarge because of the generation of porous,the negatively shifted conduction band position thermodynamically supplies stronger motivation for water reduction.Photoelectricity tests reveal that the photo‐induced electron density was increased after C‐I codoping modification.Also,the recombination rate of electron‐hole pairs is remarkably inhibited.The catalysts with moderate C‐I codoing content perform sharply enhanced photocatalytic H2 evolution activity under visible light irradiation.A H2 evolution rate of 168.2μmol/h was achieved and it was more than 9.8 times higher than pristine carbon nitride.This study demonstrates a novel non‐metal doping strategy for synthesis and optimization of polymer semiconductor with gratifying photocatalytic H2 evolution performance from water hydrolysis.