Microstructure Regulation And Photoelectric Synergy Mechanism Of Semiconductor Minerals With Broad Band Gap

With the rapid development of global industrialization,environmental pollution and ecological destruction in the worldwide are becoming more and more serious.So the urgenc y of environmental pollution prevention and control has become increasingl y promine nt.All countries are vigorousl y ex ploring new technologies and new methods of environmental pollution control in order to achieve sustainable development.Among numerous environmentalpollutioncontroltechnologies,theheterogeneous photocatal ytic react i on of semiconductor minerals has attracted wide attention due to direct use of sunlight,mild reaction conditions and deep purification of pollutants.Thus,it has become an ideal environmental pollution control technology,and is also one of the most acti ve research directions in the field of Environmental Science in recent years.However,the application of this technology is not advanced due to two crucial deficiencies,one is its wide band gap,which limits its response range in sunlight.And the other is a high recombination rate of photogenerated carriers that limits the utilization rate for them.The photoelectric conversion properties of semiconductor minerals are closel y related to their microstructures.As everyone knows,the t ype of crystal phase determines the difficult y of carrier transition;doping or not determines the semiconductor mechanism;the band structure determines the range of the spectral response;the surface morphology determines the carrier response and reactive activit y.It is possible to optimize the photoelectric conversion performance onl y b y effectivel y adjusting and controlling the structural factors as described above.Semiconductor minerals of the ox ide?TiO ₂?and sulfide?ZnS?with the wide band gap,which have been widel y studied,are ex pected to achieve full-band solar response through the band regulation.In ad dition,natural semiconductor minerals of rutile and sphalerite with abundant reserves in nature are ex pected to greatl y reduce the cost of photoelectric conversion materials through replacing the artificial s ynthesis with the natural semiconductor mineral.Therefore,it is of great practical significance to utilize semiconductor minerals to control environmental pollution through designing and s ynthesizing them to u tilize full range sunlight,developing and utilizing their environmental attributes and exploring and clarifyin g the relationship between the microstructure and the photoelectric conversion propert y of semiconductor minerals.Based on the potential application value of photoelectric conversion of semiconductor mineral in the field of environmental pollution control,in order to explore methods of low-cost semiconductor mineral construction and improve its photoelectric conversi on efficiency through the regulation of micro-structure,two kinds of semiconductor minerals with broad band gap,titanium dioxide and zinc sulfide,which are important application prospects in the field of environmental pollution control,are selected as the research objects in this paper.On the basis of identifyin g the mineral propert y and semiconductor characteristics,compounds of s ynthetic and natural minerals wereprepared.Theirmicrostructuresarecontrolledusingthe heterophase junction with the same chemical composition,active crystal-facet nanoarrays,electronic promoter of graphene and vacancy to improve the separation and transmission efficiency of photogenerated carriers.The contribution mechanism of various factors to photoelectric efficiency was studied b y photoelectrochemical s ystem.The photocatal ytic degradation of meth yl orange?MO?and the photocatal ytic reduction of chromium???using semiconductor minerals,the photocatal ytic performance and kinetic characteristics and the photocatal ytic s ynergistic mechanism were studied.1.Anatase/natural rutile?A/NR?het erophase junction was prepared,and its s ynergistic mechanism was studied.A/NR with the photoelectric s ynergistic-structure of homogeneous pol ycr ystalline was obtained,which was anatase nanoparticles gr owing on natural rutile sheets b y microwave h ydrothermal method.The results show that the photoelectric conversion performance of A/NR1:2 is 20.1 times as that of natural rutile and 3.8 times as that of pure titanium dioxide photoelectrode.The photocatal ytic degradation?MO?performance of A/NR 1:2 under visible light is 55.75%at480 min,and the photocatal ytic reduction of Cr???is 54.70%at 480 min under visible light.The mechanism analysis shows that the main s ynergism reasons of the pol ycrystalline A/NR are as follows:firstly,the lamellar granular microstructures increase the light-absorbing area and increase the light absorption ratio;secondl y,the homogeneous heterophase junctions composed of anatase and natural rutile improve the separation efficiency of photogenerated carriers;thirdl y,the el ectron color centers produced b y lattice distortion due to Fe-containing impurities in the natural rutile become capture centers,further reducing the photogenerated electron-hole recombination rate.2.Anatase arrays with the active crystal facet were s ynthesized,and their s ynergistic mechanism was studied.Anatase arrays with different exposure ratios of?001?,?010?and?101?crystal planes were obtained in d ifferent polarit y solvents using low-temperature solvothermal method.The results show that the different concentration of crystal surface regulators at liquid-liquid interface caused b y the polarit y of solvents is the key factor,which affects the growth units and the ratio of active cryst al facets.The photoelectric conversion efficiency of A001 array prepared in cyclohex ane with?001?crystal facet exposed is 0.25%,which is 6.3 times as that of pure titanium dioxide photocathode.A001 arrays have high photocatal ytic abilit y to photocatal ytic degrade of MO,which is 92.45%in 300 minutes,and A010arrays with exposed?010?crystal facet prepared in toluene have high photocatal ytic performance to photocatal ytic reduce of Cr???,which is 61.92%in 300 min utes.The s ynerg y mechanism involves the following aspects:the s ynergistic effects of the built-in electric field caused b y the different charge densit y on different crystal facets,the improvement of photogenerated electron-hole separation driven b y diff erent conduction-band and valence-band potentials in the different crystal facets and the orientation of electron and hole flow induced b y the ordered structure of the array are the intrinsic mechanisms of the improvement of photoelectric efficiency.3.Reduced graphene oxide/anatase arrays?RGOx/A001?were prepared,and the crystal facet regulation and the syn ergistic mechanism were studied.The photoelectric syn ergistic structure of reduced graphene oxide/anatase arrays was constructed using low temperature solvothermal method in cyclohex ane.The results show that the photoelectric conversion efficiency of RGO_0.8/A001 with reduced graphene oxide content of 0.8 wt%is 2.0 times as that of A001 arrays and 12.3 times as that of pure titanium dioxide photoelectrode.The photocatal ytic degradation efficiency o f MO b y RGO_0.8/A001 is 88.64%in 180 min,and the photocatal ytic reduction efficiency of Cr???is 63.68%in 180 min.The s yn ergism mechanism of photoelectric efficiency is as follows:firstl y,t hinning growth units increase the proportion of active crystal facet?001?exposure,and the ex posure of active crystal facets is beneficial to the separation of photogenerated electrons and holes in the cell space;secondl y,the introduction of GO,electr onic assistant,is conducive to improving the electron transport efficiency and further improving the separation efficiency of photogenerated electrons and holes.4.Active crystal-facet wurtzite/natural sphalerite(W _x S_1-x)was prepared,and its photoelect ric s yn ergistic mechanism was studied.The photoelectric s ynergistic structure of wurtzite/natural sphalerite was prepared b y h ydrothermal method,which is nano hierarchical sphere grown on lamellar cleavage surface.The nano hierarchical-spheres were fo rmed b y self-assembl y of nano columns with active crystal facet?002?exposed.The photoelectric conversion performance of W _0.4S_0.6 is 5.0 times as that of natural sphalerite,and 3.8 times as that of pure titanium diox ide.The photocatal ytic degradation p erformance of MO and photocatal ytic reduction performance of Cr???using W _0.4S_0.6 are 89.10%in 360 min and 97.11%in30 min under UV light,respectivel y.The enhancement mechanism of photoelectric efficiency is as follows:firstl y,the homogeneous hetero geneous junction of wurtzite/natural sphalerite is beneficial to the enhancement of the separation efficiency of photogenerat ed carriers;secondl y,the nano hierarchical-sphere with active crystal facet ex posed not onl y improves the light capture rate,bu t also facilitates the separation of photogenerated electrons and holes in crystal plane space;thirdl y,the vacancies of Zn and S occurring in the mineralization process of natural sphalerite act as the separation center of photogenerated carriers,which can further improve the photoelectric conversion efficiency.5.Reduced graphene ox ide/wurtzite?RGOx/W?with active crystal facet ex posed was prepared,and its photoelectric s ynergistic mechanism was studied.Reduced g raphene oxide/active surface exposed wurtzite was obtained b y photoreduction and in situ h ydrothermal method,whose micromorphology was the self-assembled nano hierarchical-spheres uniforml y distributed on the graphene lamellar structure.The photoelectric conversion efficiency of RGO _{G 0.5}/W is 0.19%,which is 4.9 times as that of pure titanium dioxide photocathode.The photocatal ytic degradation of MO using RGO_G0.50/W is 92.18%in 240 min,and the photocatal ytic reduction of Cr???is 98.64%in 30 min.The mechanism of the photoelectric efficiency is as follows:firstl y,self-assembled nanospheres can not onl y improve the light capture rate,but also facilitate the separation of photogenerated electrons and holes in the crystal plane space;secondl y,the introduction of electronic assistant GO can improve the electron transport efficiency and further enhance the separation efficiency of photogenerated electrons and holes.