The Preparation,Modification And Photocatalytic Performance Of CdS Nanobelts With Exposed Reactive(002)facets

CdS,with energy gap of 2.4 e V,can be excited by the visible light less than 520 nm wavelength,which indicates it is a good photocatalyst with higher activities.However,there are still some defects limiting its application: Firstly,the heavy metal Cd is a toxic material,which might pollute the environment and very difficult in recycling;Secondly,the photocorrosion of pure CdS is very serious,and the activities of catalyst will be gradually reduced on the visible light irradiation;Thirdly,the recombination of photoinduced electron-hole pairs of bulk CdS catalyst is very serious,leading to the low photocatalytic quantum efficiency.In order to solve the above problems,many researchers modified the material via different methods.While many progresses have been gained,there is still a big distance for the CdS photocatalytic technology to achieve the actual application level.In this paper,through the one-step method,the ultrathin CdS nanobelts with high catalytic activities and exposed high-energy（002）crystal plane were successfully synthesized,on basis of which,it was further modified using the methods including cocatalyst loading,carbon coating,and C3N4 compounding.Specific research contents are stated as follows:（1）Using CdCl₂·2.5H2 O and S powder as raw materials,ultrathin CdS nanobelts with exposed high-energy（002）crystal plane were prepared by the solvothermal method.The results of BET and PL tests have shown that,ultrathin CdS nanobelts have higher specific surface area and lower fluorescence intensity compared with CdS nanoparticles.The result of photocatalytic hydrogen production test has shown that,under the visible light irradiation the wave length of which is more than 420 nm,the hydregon producion rate of CdS nanobelts with exposed high-energy（002）crystal plane reaches 59.52 mmol g-1 h-1,which is about 160 times as much as that of the CdS nanoparticles.The reasons why the CdS nanobelts with exposed high-energy（002）crystal plane have high catalytic activities are as follows: a)The surface of CdS nanobelts with exposed high-energy（002）crystal plane has unsaturated-coordination S and Cd,corresponding to “built-in electric field”,which can effectively increase transmission speed of photongenerated carriers and achieve spatial isolation beam transmission of photo-induced charge carriers;b)ultrathin thickness shortens the distance of photoinduced charge carriers to nanobelt surface,which can effectively resist bulk phase composition of electron-hole pairs;c)larger specific surface area and exposed（002）high-activity crystal plane can provide more high-activity reaction sites,increasing the transfer speed of photoinduced charge carriers and reducing the surface recombination of photongenerated carriers.（2）Using the CdS nanobelts with exposed high-energy（002）crystal plane and（NH4）2MoS4 as raw materials,the CdS nanobelts with high-energy（002）crystal plane loaded with the cocatalyst were prepared by the photodeposition method.The result of PL test has shown that the fluorescence intensity of sample CdS/MoS₂ is significantly reduced.The electrochemical test shows that the photocurrent of CdS-0.4%MoS₂ reaches 14.3 μA/cm2,which is two times as much as that of the pure CdS nanobelts.The photocatalytic hydrogen production test shows that the hydrogen production rate of CdS-0.4%MoS₂ reaches 92.97 mmol g-1 h-1 under the visible light irradiation,which is approximately 1.5 times as much as that of the CdS nanobelts.Many active sites are provided on the CdS nanobelt surface after CdS nanobelts are loaded with cocatalyst,accelerating the reduction of protons.Thus,the CdS nanobelts with exposed high-energy（002）crystal plane loaded with MoS₂ present better visible photocatalytic hydrogen production performance.（3）Using CdS nanobelts and glucose as raw materials,carbon-coated CdS nanobelts were prepared by hydrothermal method.The results of UV-vis and PL tests have shown the red shift of absorption edge of carbon-coated samples and significant reduction of fluorescence intensity.The photoelectrochemical test shows an increase of photocurrent of CdS-C-0.2,reaching 10.5 μA/cm2.The photodegradable rhodamine B test shows that the time of CdS-C-0.2 degradation is significantly reduced.The carbon-layer conductivity is good,which can effectively transfer photoinduced electrons produced by photocatalyst and promote separation of photogenerated electron-hole pairs.The above factors make the carbon-coated CdS nanobelts materials exhibit more excellent photocatalytic performance.（4）Using CdCl₂·2.5H2 O,S powder,and C3N4 as raw materials,CdS/C3N4 composite materials were prepared via solvothermal method.The result of UV-vis test has shown that the absorption edge of composite materials has been significantly changed.In the photodegradable rhodamine B test,the required time of 25%CdS-C3N4 composite materials in photodegradation of RhB has been significantly reduced.The match between energy level of two materials leads to respective transformation of photo-induced electron-hole pairs to two semiconductors,which extends the length of photo-induced electrons and holes thus greatly improving the photocatalytic performance of composite materials.