等浓度的氯化铵和硫酸铵溶液哪个pH高

有中学化学参考资料题:0.10 mol/L的NH4Cl和(NH4)2SO4溶液哪个pH值高?这似乎是个中学生可做的简单题目,仔细考虑不是如此.如果简单地认为盐酸和硫酸都是强酸,而硫酸是二元酸,硫酸铵溶液中铵盐浓度为0.20 mol/L,那么NH4Cl溶液pH高,那是不妥的.硫酸是二元酸,第一个氢离子能完全电离,第二个氢离子部分电离,如此考虑情况怎么样呢?是不是答案发生变化?这要通过计算来说明.     

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin(Sn)halide-based perovskite solar cells(PSCs)fall a large gap behind those of lead halide-based PSCs,mainly because of poor film quality of the former.Here we report an efficient strategy based on a simple secondary crystallization growth(SCG)technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface.They were discovered to enhance the film crystallinity and suppress the oxidation of Sn²⁺remarkably,hence reduce trap state density and non-irradiative recombination in the absorber films.Furthermore,the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces.Consequently,a champion device efficiency of 8.07% was achieved alo ng with significant enhancements in VOC and JSC,in contrast to 5.35% of the control device value.Moreover,the SCG film-based devices also exhibit superior stability comparing with the control one.This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.     

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO₂ and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm² and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.     

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_1/2) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.     

Recent Advances of Pure Organic Room Temperature Phosphorescence Materials for Bioimaging Applications

Bioimaging,as a powerful and helpful tool,which allows people to investigate deeply within living organisms,has contributed a lot for both clinical theranostics and scientific research.Pure organic room temperature phosphorescence(RTP)materials with the unique features of ultralong luminescence lifetime and large Stokes shift,can efficiently avoid biological autofluorescence and scattered light through a time-resolved imaging modality,and thus are attracting increasing attention.This review classifies pure organic RTP materials into three categories,including small molecule RTP materials,polymer RTP materials and supramolecular RTP materials,and summarizes the recent advances of pure organic RTP materials for bioimaging applications.     

Stabilizing High-voltage Cathode Materials for Next-generation Li-ion Batteries

The pressing demand for high-energy/power lithium-ion batteries requires the deployment of cathode materials with higher capacity and output voltage.Despite more than ten years of research,high-voltage cathode mate-rials,such as high-voltage layered oxides,spinel LiNi0.5Mn1.5O4,and high-voltage polyanionic compounds still cannot be commercially viable due to the instabilities of standard electrolytes,cathode materials,and cathode electrolyte interphases under high-voltage operation.This paper summarizes the recent advances in addressing the surface and interface issues haunting the application of high-voltage cathode materials.The understanding of the limitations and advantages of different modification protocols will direct the future endeavours on advancing high-energy/power lithium-ion batteries.     

Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.     

Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated.Favorable vertical phase distribution with donors(acceptors)accumulated(depleted)at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6.In addition,N2200 is gradiently distributed in the vertical direction in the ternary blend film.Various measurements were carried out to study the effects of N2200 on the binary systems.It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films,which is beneficial for the charge transport and collection.All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells(OSCs),and power conversion efficiencies(PCEs)of 12.5%and 16.42%were obtained for the ternary OSCs,respectively.This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.     

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_0.5Co_0.2Mn_0.3O₂ cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.     

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^-2 and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^-2 but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^-2;the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^-2(246.9 mAh g^-1) at 3 mA cm^-2 and outstanding rate performance with 84.7% retention at 30 mA cm^-2,suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^-2 at the power density of 2.14 mW cm^-2 with excellent electrochemical cycling stability.     

二维/二维FeNi-LDH/g-C3N4复合光催化剂用于促进CO2光还原反应

Photocatalytic reduction of carbon dioxide into chemical fuels is a promising route to generate renewable energy and curtail the greenhouse effect. Therefore, various photocatalysts have been intensively studied for this purpose. Among them, g-C₃N₄, a 2D metal-free semiconductor, has been a promising photocatalyst because of its unique properties, such as high chemical stability, suitable electronic structure, and facile preparation. However, pristine g-C₃N₄ suffers from low solar energy conversion efficiency, owing to its small specific surface area and extensive charge recombination. Therefore, designing g-C₃N₄ (CN) nanosheets with a large specific surface area is an effective strategy for enhancing the CO₂ reduction performance. Unfortunately, the performance of CN nanosheets remains moderate due to the aforementioned charge recombination. To counter this issue, loading a cocatalyst (especially a two-dimensional (2D) one) can enable effective electron migration and suppress electron-hole recombination during photo-irradiation. Herein, CN nanosheets with a large specific surface area (97 m²·g^-1) were synthesized by a two-step calcination method, using urea as the precursor. Following this, a 2D/2D FeNi-LDH/g-C₃N₄ hybrid photocatalyst was obtained by loading a FeNi layered double hydroxide (FeNi-LDH) cocatalyst onto CN nanosheets by a simple hydrothermal method. It was found that the production rate of methanol from photocatalytic CO₂ reduction over the FeNi-LDH/g-C₃N₄ composite is significantly higher than that of pristine CN. Following a series of characterization and analysis, it was demonstrated that the FeNi-LDH/g-C₃N₄ composite photocatalyst exhibited enhanced photo-absorption, which was ascribed to the excellent light absorption ability of FeNi-LDH. The CO₂ adsorption capacity of the FeNi-LDH/g-C₃N₄ hybrid photocatalyst improved, owing to the large specific surface area and alkaline nature of FeNi-LDH. More importantly, the introduction of FeNi-LDH on the CN nanosheet surface led to the formation of a 2D/2D heterojunction with a large contact area at the interface, which could promote the interfacial separation of charge carriers and effectively inhibit the recombination of the photogenerated electrons and holes. This subsequently resulted in the enhancement of the CO₂ photo-reduction activity. In addition, by altering the loading amount of FeNi-LDH for photocatalytic performance evaluation, it was found that the optimal loading amount was 4% (w, mass fraction), with a methanol production rate of 1.64 μmol·h^-1·g^-1 (approximately 6 times that of pure CN). This study provides an effective strategy to improve the photocatalytic CO₂ reduction activity of g-C₃N₄ by employing 2D layered double hydroxide as the cocatalyst. It also proposes a protocol for the successful design of 2D/2D photocatalysts for solar energy conversion.      

MOFs基材料在光催化CO2还原中的应用

系统总结了金属有机框架(MOFs)基材料在光催化还原CO₂中的最新研究进展, 其中包括MOFs直接作为光催化剂和作为复合光催化2个主要部分, 讨论了MOFs基光催化剂在催化还原CO₂方面展现出的独特优势, 并对MOFs基光催化剂的结构稳定性与CO₂转化效率等问题进行讨论与分析, 对未来发展趋势进行了展望.     

基于氨基化煤基碳点的复合光催化剂的制备及对CO2还原的催化性能

采用过氧化氢氧化法剥离出煤炭结构中的晶体碳[煤基碳点(CDs)], 并通过亚硫酰氯氯化及乙二胺钝化等步骤对其进行氨基化修饰, 制得N, S共掺杂的氨基化煤基碳点(NH₂-CDs), 再利用其表面的氨基和含氧基等官能团的配位及分散作用, 将由氯化铜原位还原得到的氧化亚铜(Cu₂O)纳米粒子包覆于其中, 制备了复合催化剂Cu₂O/NH₂-CDs, 表征了其结构和形貌, 并考察了其可见光催化还原CO₂/H₂O的性能. 结果发现, NH₂-CDs的存在使复合催化剂不仅具备了较强的CO₂吸附性能, 而且还具有了高效的电子-空穴对分离和电子转移能力, 从而表现出优异的光催化还原CO₂制备HCOOH的性能. 反应6 h时, 产物HCOOH的量为2582.4 μmol/g cat, 约为同条件下纯Cu₂O作为光催化剂时产物HCOOH产率的7.3倍.     

空心NiCo2S4纳米球助催化剂担载ZnIn2S4纳米片用于可见光催化制氢

纳米片与空心球上之间的合理界面调控是开发高效太阳能制氢光催化剂的潜在策略。在各类光催化材料中,金属硫化物由于具有相对较窄的带隙和优越的可见光响应能力而被广泛研究。ZnIn₂S₄是一种层状的三元过渡金属半导体光催化剂,其带隙可控(约2.4 eV)。在众多金属硫化物光催化剂中,ZnIn₂S₄引起了广泛兴趣。然而,单纯的ZnIn₂S₄光催化活性仍然相对较差,主要是因为光生载流子的复合率较高、迁移速率较慢。在半导体光催化剂上负载助催化剂是提升光催化剂性能的一种有效方法,因为它不仅可以加速光生电子和空穴的分离,而且还可以降低质子还原反应的活化能。作为一种三元过渡金属硫化物,NiCo₂S₄表现出较高的导电性、较低的电负性、丰富的氧化还原特性以及优越的电催化活性。这些特性表明,NiCo₂S₄可以作为光催化制氢的助催化剂,以加速电荷分离和转移。此外,NiCo₂S₄和ZnIn₂S₄都属于三元尖晶石的晶体结构,这可能有助于构建具有紧密界面接触的NiCo₂S₄/ZnIn₂S₄复合物,从而提高光催化性能。本文中,将超薄ZnIn₂S₄纳米片原位生长到非贵金属助催化剂NiCo₂S₄空心球上,形成具有强耦合界面和可见光吸收的NiCo₂S₄@ZnIn₂S₄分级空心异质结构光催化剂。最优NiCo₂S₄@ZnIn₂S₄复合样品(NiCo₂S₄含量：ca. 3.1%)的析氢速率高达78 μmol·h^-1,约是纳米片组装ZnIn₂S₄光催化剂析氢速率的9倍、约是1% (w, 质量分数)Pt/ZnIn₂S₄样品析氢速率的3倍。此外,该复合光催化剂在反应中表现出良好的稳定性。荧光和电化学测试结果表明,NiCo₂S₄空心球是一种有效的助催化剂,可促进光生载流子的分离和传输,并降低析氢反应的活化能。最后,提出了NiCo₂S₄@ZnIn₂S₄光催化析氢的可能反应机理。在NiCo₂S₄@ZnIn₂S₄复合光催化剂中,具有高导电性的NiCo₂S₄助催化剂可快速接受ZnIn₂S₄上的光生电子,用以还原质子生成氢气,而电子牺牲剂TEOA捕获光生空穴,进而完成光催化氧化还原循环。该研究有望为基于纳米片为次级结构的分级空心异质结光催化剂的设计合成及其光催化制氢研究提供一定的指导。     

Ni2P纳米片用于光催化二氧化碳还原

Artificial photosynthesis is an ideal method for solar-to-chemical energy conversion, wherein solar energy is stored in the form of chemical bonds of solar fuels. In particular, the photocatalytic reduction of CO₂ has attracted considerable attention due to its dual benefits of fossil fuel production and CO₂ pollution reduction. However, CO₂ is a comparatively stable molecule and its photoreduction is thermodynamically and kinetically challenging. Thus, the photocatalytic efficiency of CO₂ reduction is far below the level of industrial applications. Therefore, development of low-cost cocatalysts is crucial for significantly decreasing the activation energy of CO₂ to achieving efficient photocatalytic CO₂ reduction. Herein, we have reported the use of a Ni₂P material that can serve as a robust cocatalyst by cooperating with a photosensitizer for the photoconversion of CO₂. An effective strategy for engineering Ni₂P in an ultrathin layered structure has been proposed to improve the CO₂ adsorption capability and decrease the CO₂ activation energy, resulting in efficient CO₂ reduction. A series of physicochemical characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM) were used to demonstrate the successful preparation of ultrathin Ni₂P nanosheets. The XRD and XPS results confirm the successful synthesis of Ni₂P from Ni(OH)₂ by a low temperature phosphidation process. According to the TEM images, the prepared Ni₂P nanosheets exhibit a 2D and near-transparent sheet-like structure, suggesting their ultrathin thickness. The AFM images further demonstrated this result and also showed that the height of the Ni₂P nanosheets is ca 1.5 nm. The photoluminescence (PL) spectroscopy results revealed that the Ni₂P material could efficiently promote the separation of the photogenerated electrons and holes in [Ru(bpy)₃]Cl₂·6H₂O. More importantly, the Ni₂P nanosheets could more efficiently promote the charge transfer and charge separation rate of [Ru(bpy)₃]Cl₂·6H₂O compared with the Ni₂P particles. In addition, the electrochemical experiments revealed that the Ni₂P nanosheets, with their high active surface area and charge conductivity, can provide more active centers for CO₂ conversion and accelerate the interfacial reaction dynamics. These results strongly suggest that the Ni₂P nanosheets are a promising material for photocatalytic CO₂ reduction, and can achieve a CO generation rate of 64.8 μmol·h^-1, which is 4.4 times higher than that of the Ni₂P particles. In addition, the XRD and XPS measurements of the used Ni₂P nanosheets after the six cycles of the photocatalytic CO₂ reduction reaction demonstrated their high stability. Overall, this study offers a new function for the 2D transition-metal phosphide catalysts in photocatalytic CO₂ reduction.     

基于CdS和CdSe纳米半导体材料的可见光催化二氧化碳还原研究进展

Carbon dioxide (CO₂) is one of the main greenhouse gases in the atmosphere. The conversion of CO₂ into solar fuels (CO, HCOOH, CH₄, CH₃OH, etc.) using artificial photosynthetic systems is an ideal way to utilize CO₂ as a resource and reduce CO₂ emissions. A typical artificial photosynthetic system is composed of three key components: a photosensitizer (PS) to harvest visible light, a catalyst (C) to catalyze CO₂ or protons into carbon-based fuels or H₂, respectively, and a sacrificial electron donor (SED) to consume the holes generated in the PS. In most cases, the PS and catalyst are two different components of a system. However, some components that possess both light harvesting and redox catalysis functionalities, e.g., nano-semiconductors, are referred to as photocatalysts. During photocatalysis, the PS is typically excited by photons to generate excited electrons. The excited electrons in the PS are transferred to the catalyst to generate a reduced catalyst. The reduced catalyst is used as an active intermediate to perform CO₂ binding and transformation. The PS can be recovered through a reaction with the SED. Nano-semiconductors have been used as photosensitizers and/or photocatalysts in photocatalytic CO₂ reduction systems owing to their excellent photophysical and photochemical properties and photostability. CdS and CdSe nano-semiconductors, such as quantum dots, nanorods, and nanosheets, have been widely used in the construction of photocatalytic CO₂ reduction systems. Systems based on CdS or CdSe nano-semiconductors can be classified into three categories. The first category is systems based on CdS or CdSe photocatalysts. In these systems, CdS or CdSe nano-semiconductors function as photocatalysts to catalyze CO₂ reduction without a co-catalyst under visible-light irradiation. The CO₂ reduction reaction occurs at the surface of the CdS or CdSe nano-semiconductors. The second category is systems based on CdS or CdSe composite photocatalysts. CdS or CdSe nano-semiconductors are combined with functional materials, such as reduced graphene oxide or TiO₂, to prepare composite photocatalysts. These composite photocatalysts are expected to improve the lifetime of the charge separation state and inhibit the photocorrosion of the nano-semiconductors during photocatalysis. The third category is hybrid systems containing a CdS nano-semiconductor and molecular catalysts, such as nickel and cobalt complexes and iron porphyrin. In these hybrid systems, CdS functions as a photosensitizer and the CO₂ reduction reaction occurs at the molecular catalyst. This review article introduces the construction of artificial photosynthetic systems and the photocatalytic mechanism of nano-semiconductors, and summarizes the representative works in the three aforementioned categories of systems. Finally, the challenges of nano-semiconductors for photocatalytic CO₂ reduction are discussed.     

SnO_2/TiO_2纳米管复合光催化剂的性能及失活再生

基于微波水热法和微乳液法合成SnO2/TiO2纳米管复合光催化剂.通过X射线衍射(XRD)、配有能量色散X射线光谱仪(EDX)的透射电镜(TEM)和电化学手段对光催化剂进行表征.以甲苯为模型污染物,考察光催化剂在紫外光(UV)和真空远紫外光(VUV)下的性能及失活再生.结果表明,SnO2/TiO2纳米管复合光催化剂形成三元异质结(锐钛矿相TiO2(A-TiO2)/金红石相TiO2(R-TiO2)、A-TiO2/SnO2和R-TiO2/SnO2异质结),促使光生电子-空穴对的有效分离,提高光催化活性.SnO2/TiO2表现出最佳的光催化性能,UV和VUV条件下的甲苯降解率均达100%,CO2生成速率(k2)均为P25的3倍左右.但由于UV光照矿化能力不足,中间产物易在催化剂表面累积.随着UV光照时间的增加,SnO2/TiO2逐渐失活,20 h后k2由138.5 mg·m-3·h-1下降到76.1 mg·m-3·h-1.利用VUV再生失活的SnO2/TiO2,过程中产生的·OH、O2-·、O(1D)、O(3P)、O3等活性物质可氧化吸附于催化剂活性位的难降解中间产物,使催化剂得以再生,12 h后k2恢复到143.6 mg·m-3·h-1.UV和VUV的协同效应使UV降解耦合VUV再生成为一种可持续的光催化降解污染物模式.     

棒状金属有机框架结构PCN-222(Cu)/TiO2复合材料的制备及其高效光催化CO2还原性能

The photocatalytic reduction of CO₂ has attracted considerable attention owing to the dual suppression of environmental pollution and energy shortage. The technology uses solar energy to convert carbon dioxide into hydrocarbon fuel, which is of great significance for achieving the carbon cycle. The development of low-cost photocatalytic materials is critical to achieving efficient solar energy to fuels conversion. One of the most commonly employed photocatalysts is TiO₂. However, it suffers from broad band gap as well as the recombination of photo-excited holes and electron. Hence, in this work, we report the photochemical reduction of CO₂ using rod-like PCN-222(Cu)/TiO₂ composites as photocatalyst through a simple hydrothermal method, in which TiO₂ nanoparticles are anchored at the interface of the SiC rod PCN-222(Cu). Multiple characterization techniques were used to analyze the structure, morphology, and properties of the PCN-222(Cu)/TiO₂ composite. A series of characterizations including X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy, photo-electrochemical, and photoluminescence (PL) confirm the successful preparation of PCN-222(Cu)/TiO₂ composites. SEM reveals that the TiO₂ nanoparticles are uniformly distributed on the surface of the rod-shaped PCN-222(Cu)/TiO₂. XRD results show that PCN-222(Cu) and PCN-222(Cu)/TiO₂ composite photocatalysts with good crystal structure were successfully synthesized. According to the DRS results, the prepared PCN-222(Cu)/TiO₂ composite samples exhibit characteristic absorption peaks of metalloporphyrins in the visible region. PL spectroscopy, transient photocurrent response, and electrochemical impedance spectroscopy further confirm that the rod-like PCN-222(Cu)/TiO₂ samples have high electron-hole pair separation efficiency. By controlling the mass ratio of PCN-222(Cu) and TiO₂, the photocatalytic CO₂ reduction performance test shows that the 10% PCN-222(Cu)/TiO₂ composite achieves optimal catalytic performance, yielding 13.24 μmol·g⁻¹·h⁻¹ CO and 1.73 μmol·g⁻¹·h⁻¹ CH₄, respectively. All the rod-like PCN-222(Cu)/TiO₂ composites exhibit better photocatalytic CO₂ activity than that of TiO₂ nanoparticles or PCN-222(Cu) under the illumination of xenon lamps, which is attributed to charge transport and electron-hole separation capabilities. After three test cycles, the catalytic activity of PCN-222(Cu)/TiO₂ photocatalyst was virtually unchanged. The reduction yield of the catalyst increased for 8 h under continuous illumination, indicating that PCN-222(Cu)/TiO₂ composites have acceptable stability. The estimation of the band gap curve and the Mote-Schottky curve test show that the lowest unoccupied molecular orbital position of PCN-222(Cu) is more negative than the TiO₂ of the conduction band; hence, a possible photocatalytic reaction mechanism of the PCN-222(Cu)/TiO₂ composite is proposed. This study provides a new strategy for the integration of metal-organic frameworks and oxide semiconductors to construct efficient photocatalytic systems.     

理论计算研究二维/二维BP/g-C3N4异质结的光催化CO2还原性能

Photocatalytic reduction of CO₂ to hydrocarbon compounds is a promising method for addressing energy shortages and environmental pollution. Considerable efforts have been devoted to exploring valid strategies to enhance photocatalytic efficiency. Among various modification methods, the hybridization of different photocatalysts is effective for addressing the shortcomings of a single photocatalyst and enhancing its CO₂ reduction performance. In addition, metal-free materials such as g-C₃N₄ and black phosphorus (BP) are attractive because of their unique structures and electronic properties. Many experimental results have verified the superior photocatalytic activity of a BP/g-C₃N₄ composite. However, theoretical understanding of the intrinsic mechanism of the activity enhancement is still lacking. Herein, the geometric structures, optical absorption, electronic properties, and CO₂ reduction reaction processes of 2D/2D BP/g-C₃N₄ composite models are investigated using density functional theory calculations. The composite model consists of a monolayer of BP and a tri-s-triazine-based monolayer of g-C₃N₄. Based on the calculated work function, it is inferred that electrons transfer from g-C₃N₄ to BP owing to the higher Fermi level of g-C₃N₄ compared with that of BP. Furthermore, the charge density difference suggests the formation of a built-in electric field at the interface, which is conducive to the separation of photogenerated electron-hole pairs. The optical absorption coefficient demonstrates that the light absorption of the composite is significantly higher than that of its single-component counterpart. Integrated analysis of the band edge potential and interfacial electronic interaction indicates that the migration of photogenerated charge carriers in the BP/g-C₃N₄ hybrid follows the S-scheme photocatalytic mechanism. Under visible-light irradiation, the photogenerated electrons on BP recombine with the photogenerated holes on g-C₃N₄, leaving photogenerated electrons and holes in the conduction band of g-C₃N₄ and the valence band of BP, respectively. Compared with pristine g-C₃N₄, this S-scheme heterojunction allows efficient separation of photogenerated charge carriers while effectively preserving strong redox abilities. Additionally, the possible reaction path for CO₂ reduction on g-C₃N₄ and BP/g-C₃N₄ is discussed by computing the free energy of each step. It was found that CO₂ reduction on the composite occurs most readily on the g-C₃N₄ side. The reaction path on the composite is different from that on g-C₃N₄. The heterojunction reduces the maximum energy barrier for CO₂ reduction from 1.48 to 1.22 eV, following the optimal reaction path. Consequently, the BP/g-C₃N₄ heterojunction is theoretically proven to be an excellent CO₂ reduction photocatalyst. This work is helpful for understanding the effect of BP modification on the photocatalytic activity of g-C₃N₄. It also provides a theoretical basis for the design of other high-performance CO₂ reduction photocatalysts.      

Enhanced Charge Separation of α-Bi2O3-BiOI Hollow Nanotube for Photodegradation Antibiotic Under Visible Light

It is highly desirable to exploit semiconductor materials with high photocatalytic degradation activity, especially bismuth oxyhalide semiconductor photocatalysts with special layered structure and suitable bandgap width. The low utilization rate of visible light and high recombination rate of photogenerated electron-hole of BiOI photocatalyst severely restrict its development. Herein, a heterojunction photocatalyst of α-Bi₂O₃-BiOI hollow nanotube was prepared by electrospinning method, solvothermal method and ion-exchange method. The α-Bi₂O₃-BiOI(BB-4, the stirring time of Bi₂O₃ in KI solution was 4 h) exhibited the best photocatalytic performance towards degrading the tetracycline hydrochloride(TC) solution, which could remove 85% of TC(10 mg/L) in 2 h under visible light irradiation. The estimated k_TC of α-Bi₂O₃-BiOI(BB-4) was ca. 3.9 and 1.8 times as much as that of α-Bi₂O₃ and pure BiOI, respectively. It indicated that the formation of α-Bi₂O₃-BiOI heterojunction can significantly improve the separation efficiency of photogenerated electron-hole pairs, therefore the photocatalytic ability was enhanced. Furthermore, a corresponding photocatalytic mechanism was proposed that ^·O₂^- radical and holes are the main active components in the photodegradation through trapping experiment.