摘要
Z型异质结是提高半导体光催化性能的一种有效途径,因为Z型异质结具有抑制电子-空穴复合以及为2种半导体保留高氧化还原能力的双重优点。采用简单高温固化-水热法合成了具有可见光响应的新型无定型C/g-C_(3)N_(4)/Bi_(2)WO_(6)(C/C_(3)N_(4)/Bi_(2)WO_(6))Z型异质结。对制备的复合催化材料进行了系统表征,并选择盐酸四环素(TC)作为目标污染物评价其光催化性能。C/C_(3)N_(4)/Bi_(2)WO_(6)复合材料的光催化活性优于g-C_(3)N_(4)、C/C_(3)N_(4)和Bi_(2)WO_(6)。当C/C_(3)N_(4)与Bi_(2)WO_(6)的质量比为1.0:0.7时,复合催化材料(样品C/C_(3)N_(4)/Bi_(2)WO_(6)-3)的催化效率最高。C/C_(3)N_(4)/Bi_(2)WO_(6)复合光催化材料催化性能的提高可能是所形成的Z型异质结促进了光生电子-空穴对有效的分离和转移。
Introduction Photocatalysis is one of the most potential techniques to solve energy crisis and environmental pollution problems,and how to obtain photocatalysts with a greater catalytic efficiency is always a research hotspot in the photocatalysis.The heterogeneous photocatalyst is proved as a promising efficient strategy to address this issue.The heterojunction photocatalysts can be utilized to expedite the separation of photo-induced electron-hole pairs.In particular,Z-scheme heterojunctions exhibit the dual advantages of suppression of recombination of electron-hole pairs,reserving a high redox ability for both semiconductors.The visible-light-driven photocatalysts Bi_(2)WO_6 and g-C_(3)N_(4) exhibit a poor photocatalytic activity because of their fast recombination of photo-generated carriers.It is advisable to choose the g-C_(3)N_(4) and Bi_(2)WO_6 to form an all-solid-state Z-scheme photocatalytic system to obtain the higher photocatalytic performance.It is reported that carbon materials often put up a low work function when they modify the electronic and optical properties of hybrids.In this paper,a novel amorphous carbon/g-C_(3)N_(4)/Bi_(2)WO_6(C/C_(3)N_(4)/Bi_(2)WO_6)Z-scheme heterojunction with a visible light response was synthesized.The performance of C/C_(3)N_(4)/Bi_(2)WO_6 was measured by photo-degrading TC under the visible light(i.e.,≥420 nm).The as-synthesized composites played an enhanced visible-light photoactivity than the pure g-C_(3)N_(4) and Bi_(2)WO_6.Furthermore,the possible mechanism of the enhanced performance of the C/C_(3)N_(4)/Bi_(2)WO_6 composite was discussed.Methods All reagents with analytical grade were used without further purification.First,the C/C_(3)N_(4) sample was prepared by a milling/roasting method.When a mass ratio of glucose to urea was 0.1%,the as-fabricated C/C_(3)N_(4) composite exhibited an optimum photocatalytic performance.The C/C_(3)N_(4)/Bi_(2)WO_6 nanocomposites were prepared through a facile hydrothermal method.The obtained products were denoted as C/C_(3)N_(4)/Bi_(2)WO_6-1,C/C_(3)N_(4)/Bi_(2)WO_6-2,C/C_(3)N_(4)/Bi_(2)WO_6-3 and C/C_(3)N_(4)/Bi_(2)WO_6-4,when the mass ratios of C/C_(3)N_(4):Bi_(2)WO_6 were 1.0:0.1,1.0:0.4,1.0:0.7 and 1:1,respectively.For the comparison,a pure Bi_(2)WO_6 sample was synthesized through the same procedur without introducing C/C_(3)N_(4).The crystal structure was detected by X-ray diffraction with Cu K_αradiation(λ=0.15406 nm).The morphology and microstructures of the synthesized samples were investigated on high-resolution transmission electron microscopy(HRTEM).The ultraviolate-visible(UV-Vis)diffuse reflectance spectra(DRS)were taken on UV-Vis-near infrared(NIR)spectrophotometry with BaS O_(4) as a reference.The chemical composition and chemical state of C/C_(3)N_(4)/Bi_(2)WO_6 were analyzed by X-ray photoelectron spectroscopy(XPS)with Al K_αexcitation source.The photocurrent response under simulated solar light irradiation was recorded with an electrochemical workstation in a sandwich-type configuration,a Pt slice as a counter electrode,a saturated calomel electrode(SCE)as ae reference,and 0.1 mol/L Na_(2)SO_(4) solution as electrolyte.A 300 W xenon arc lamp equipped with a simulated solar light filter calibrated to 100 mW/cm^(2),which was measured with a radiometer,employed as a light source.Electrochemical impedance spectroscopy(EIS)Nyquist plots were obtained at 0.6 V with a small alternating current amplitude of 5 m V in a frequency range of0.1 Hz-10~(5)Hz.The photocatalytic activity of the C/C_(3)N_(4)/Bi_(2)WO_6 sample was determined by degrading the simulated pollutant tetracycline(TC).In the experimental setup,a 300W Xe lamp was employed as a light source and a 420 nm cut-off filter was used to provide only visible-light irradiation.The photocatalyst of 100 mg was added to 100 mL of TC solution(1×10~(-4)mol/L).Before being irradiated,the suspensions were magnetically stirred in the dark for 3 h to reach the adsorption-desorption equilibrium between photocatalysts and TC.The solution was exposed to visible light irradiation under magnetic stirring.The aliquot of 3 mL was collected from the suspension and centrifuged immediately for every 10 min.The degradation of TC was monitored by checking the absorbance at357 nm using an UV-Vis spectrometer.Results and discussion The degradation ratios of TC are 25%and 50%after irradiation for 240 min by visible-light in the presence of g-C_(3)N_(4) and Bi_(2)WO_6,respectively.Furthermore,it is clear that the C/C_(3)N_(4) composite exhibits a higher photocatalytic activity in the degradation of TC than the g-C_(3)N_(4) sample.All the C/C_(3)N_(4)/Bi_(2)WO_6 photocatalysts exhibit better photocatalytic performance than the C/C_(3)N_(4) composite and Bi_(2)WO_6 under the same experimental condition.Specifically,the photocatalytic activities of C/C_(3)N_(4)/Bi_(2)WO_6nanocomposites gradually improve as Bi_(2)WO_6 ratio increases,and the photocatalytic performance is optimal when the mass ratio of C/C_(3)N_(4):Bi_(2)WO_6 is 1.0:0.7.The photocatalytic activities decrease when Bi_(2)WO_6 ratio continues to increase.Hence,the as-prepared C/C_(3)N_(4)/Bi_(2)WO_6-3 nanocomposite has the optimum photocatalytic performance,and the maximum degradation efficiency of 97.1%is attained after the irradiation for 240 min.The improved photocatalytic performance of C/C_(3)N_(4)/Bi_(2)WO_6 composites is ascribed to the formed amorphous carbon-mediated Z-scheme heterojunction.When the heterojunction C/C_(3)N_(4)/Bi_(2)WO_6 is exposed to visible light(λ>420 nm),the electrons generated from CB of Bi_(2)WO_6 can transfer to the VB of g-C_(3)N_(4) via the amorphous carbon mediator due to the good electrical conductivity of amorphous carbon,and then annihilate with the holes induces from the VB of g-C_(3)N_(4),the photo-induced carriers can be effectively separated.Conclusion We constructed Z-scheme C/C_(3)N_(4)/Bi_(2)WO_6 heterojunction photocatalyst with enhanced photocatalytic activities in degradation of TC.When the mass ratio of C/C_(3)N_(4):Bi_(2)WO_6 was 1.0:0.7,the as-fabricated C/C_(3)N_(4)/Bi_(2)WO_6 heterojunction exhibited an optimum photocatalytic performance.The mechanism illuminated that the efficient separation of charge carriers generated by the amorphous carbon-mediated Z-scheme mechanism mainly contributed to the improved photocatalytic performance of C/C_(3)N_(4)/Bi_(2)WO_6 heterojunction.We anticipated that the results of this work could favor the application of solar energy in water pollution.
作者
郑晶静
商希礼
刘国霞
ZHENG Jingjing;SHANG Xili;LIU Guoxia(Department of Chemical Engineering and Safety,Binzhou University,Binzhou 256603,Shandong,China)
出处
《硅酸盐学报》
EI
CAS
CSCD
北大核心
2024年第1期122-132,共11页
Journal of The Chinese Ceramic Society
基金
山东省自然科学基金(ZR2020MB036,ZR2021ME246)。
关键词
无定型碳
Z型异质结
可见光光催化
钨酸铋
类石墨相氮化碳
amorphous carbon
Z-scheme-heterojunction
visible-light photocatalytic
bismuth tungstate
graphitic carbon nitride
