Polycaprolactone(PCL)scaffolds that are produced through additive manufacturing are one of the most researched bone tissue engineering structures in the field.Due to the intrinsic limitations of PCL,carbon nanomateria...Polycaprolactone(PCL)scaffolds that are produced through additive manufacturing are one of the most researched bone tissue engineering structures in the field.Due to the intrinsic limitations of PCL,carbon nanomaterials are often investigated to reinforce the PCL scaffolds.Despite several studies that have been conducted on carbon nanomaterials,such as graphene(G)and graphene oxide(GO),certain challenges remain in terms of the precise design of the biological and nonbiological properties of the scaffolds.This paper addresses this limitation by investigating both the nonbiological(element composition,surface,degradation,and thermal and mechanical properties)and biological characteristics of carbon nanomaterial-reinforced PCL scaffolds for bone tissue engineering applications.Results showed that the incorporation of G and GO increased surface properties(reduced modulus and wettability),material crystallinity,crystallization temperature,and degradation rate.However,the variations in compressive modulus,strength,surface hardness,and cell metabolic activity strongly depended on the type of reinforcement.Finally,a series of phenomenological models were developed based on experimental results to describe the variations of scaffold’s weight,fiber diameter,porosity,and mechanical properties as functions of degradation time and carbon nanomaterial concentrations.The results presented in this paper enable the design of three-dimensional(3D)bone scaffolds with tuned properties by adjusting the type and concentration of different functional fillers.展开更多
Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphe...Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-graphene as lubricating additive, with the original graphene as a comparison. The physicochemical properties and lubrication performance of the as-prepared greases were evaluated in detail. The results show that the as-prepared greases have high dropping point and colloidal stability. Furthermore, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, spilled oil, and adhesive grease greatly improves the lubrication function of grease. This research paves the way for modulating high-performance lithium complex grease to reduce the friction and wear of movable machinery.展开更多
The performance of a lubricant largely depends on the additives it involves. However, currently used additives cause severe pollution if they are burned and exhausted. Therefore, it is necessary to develop a new gener...The performance of a lubricant largely depends on the additives it involves. However, currently used additives cause severe pollution if they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide（GO） consists of only C, H and O and thus is considered to be environmentally friendly. So the tribological properties of the few-layer GO sheet as an additive in hydrocarbon base oil are investigated systematically. It is found that, with the addition of GO sheets, both the coefficient of friction（COF） and wear are decreased and the working temperature range of the lubricant is expanded in the positive direction. Moreover, GO sheets has better performance under higher sliding speed and the optimized concentration of GO sheets is determined to be 0.5wt%. After rubbing, GO is detected on the wear scars through Raman spectroscopy. And it is believed that, during the rubbing, GO sheets adhere to the sliding surfaces, behaving like protective films and preventing the sliding surfaces from contacting with each other directly. This paper proves that the GO sheet is an effective lubricant additive, illuminates the lubrication mechanism, and provides some critical parameters for the practical application of GO sheets in lubrication.展开更多
Although graphene oxide(GO)has emerged as an excellent lubricant additive in water,there remain great challenges in their practical application due to high production costs.By taking into account the low cost and also...Although graphene oxide(GO)has emerged as an excellent lubricant additive in water,there remain great challenges in their practical application due to high production costs.By taking into account the low cost and also its excellent tribological properties,it is likely that nano-SiO_(2)can be used as a lubricant additive to partially replace GO.Hence,this paper aims to explore the tribological properties of nano-SiO_(2)incorporated in GO nanofluids for partial GO replacement by investigating the friction coefficient and wear volume of the prepared SiO_(2)/GO hybrid nanofluids for magnesium alloy/steel sliding pairs.The experiments reveal that the SiO_(2)/GO hybrids retain low friction coefficients as compared to individual GO or SiO_(2)at all test conditions in this study.However,as for the bearing capacity test,all samples can provide a low wear volume under the loads of 1 and 3 N.With the increase of the normal load,there is considerable differences in the anti-wear behavior.Compared with that of individual GO nanofluids,the wear volume of the GO/SiO_(2)(mass ratio of 0.3:0.2)hybrid nanofluids was reduced by50.5%at 5 N and by 49.2%at 8 N.Furthermore,the wear volume of the GO/SiO_(2)(mass ratio of 0.3:0.2)hybrid nanofluids was reduced by46.3%under the rigorous conditions,as compared to individual GO nanofluids.The findings provide new insights into developing carbon nanomaterial-based hybrid nanofluids for magnesium alloy formation.展开更多
We investigate the fluorescence quenching of Rhodamine 6G （R6G）, a well known laser dye with a high fluorescence quantum yield, by as-synthesized graphene oxide （GO） in aqueous solution, which is found to be rathe...We investigate the fluorescence quenching of Rhodamine 6G （R6G）, a well known laser dye with a high fluorescence quantum yield, by as-synthesized graphene oxide （GO） in aqueous solution, which is found to be rather efficient. By means of steady-state and time-resolved fluorescence spectroscopy combined with detailed analysis about the linear absorption vari- ation for this R6G-GO system, the pertinent quenching mechanism has been elucidated to be a combination of dynamic and static quenching. Possible ground-state complexes be- tween R6G and GO during the static quenching have also been suggested. Furthermore, the direction of photoindueed electron transfer between R6G and GO has been discussed.展开更多
Graphene is a promising conductive additive for the lithium-ion batteries(LIBs) and shows great potential especially with its fast development of the large scale fabrication technology. This work has explored the infl...Graphene is a promising conductive additive for the lithium-ion batteries(LIBs) and shows great potential especially with its fast development of the large scale fabrication technology. This work has explored the influence of the incorporation of graphenes prepared by three typical methods on the electrochemical performance of the LiCoO_2-based cathode focusing on the choice for the effective graphene as conductive additive for the cathode of LIBs. Through the comparison of the intrinsic characteristics of graphenes and the electrochemical performance of electrodes with graphene, it is found that graphene with low disorder degree and large size is not suitable for LiCoO_2 cathodes as conductive additive. Conversely, the graphene with oxygen functional groups, relatively low surface area and proper size displays much better electrochemical performance when it is used as conductive additive. This work also demonstrates the transmission mechanism for different graphenes as conductive additives in the LiCoO_2 materials, and further reveals that the conductivity of graphene is not the only factor as conductive additives, surface chemistry and sheet size of the graphene are also essential factors which greatly influence the electrochemical performance of electrode. In addition, when combined with Super P, only 1% graphene is enough to construct an efficient conductive network in the electrode. This study also gives a new sight on the practical application of graphene as conductive additive for high performance LIBs.展开更多
The fluorescence quenching of Rhodamine 6G （R6G） by graphene oxide （GO） was interrogated by R6G fluorescence measurements using a set of controlled GO samples with varied C/O ratios as the quencher. The carbonyl g...The fluorescence quenching of Rhodamine 6G （R6G） by graphene oxide （GO） was interrogated by R6G fluorescence measurements using a set of controlled GO samples with varied C/O ratios as the quencher. The carbonyl groups on the GO nanosheet turned to play a dominant role in quenching the R6G fluorescence. The quenching in the static regime can be described by the ＂sphere of action＂ model. The significant absorption of the R6G fluorescence by the ground-state complex formed between R6G and GO was identified to be responsible for the static quenching mechanisms in quenching. This work offers the R6G/GO system. insights into the fluorescence展开更多
基金The authors wish to acknowledge Engineering and Physical Sciences Research Council(EPSRC)UK for the Global Challenges Research Fund(No.EP/R015139/1)Rosetrees Trust UK&Stoneygate Trust UK for the Enterprise Fellowship(Ref:M874).
文摘Polycaprolactone(PCL)scaffolds that are produced through additive manufacturing are one of the most researched bone tissue engineering structures in the field.Due to the intrinsic limitations of PCL,carbon nanomaterials are often investigated to reinforce the PCL scaffolds.Despite several studies that have been conducted on carbon nanomaterials,such as graphene(G)and graphene oxide(GO),certain challenges remain in terms of the precise design of the biological and nonbiological properties of the scaffolds.This paper addresses this limitation by investigating both the nonbiological(element composition,surface,degradation,and thermal and mechanical properties)and biological characteristics of carbon nanomaterial-reinforced PCL scaffolds for bone tissue engineering applications.Results showed that the incorporation of G and GO increased surface properties(reduced modulus and wettability),material crystallinity,crystallization temperature,and degradation rate.However,the variations in compressive modulus,strength,surface hardness,and cell metabolic activity strongly depended on the type of reinforcement.Finally,a series of phenomenological models were developed based on experimental results to describe the variations of scaffold’s weight,fiber diameter,porosity,and mechanical properties as functions of degradation time and carbon nanomaterial concentrations.The results presented in this paper enable the design of three-dimensional(3D)bone scaffolds with tuned properties by adjusting the type and concentration of different functional fillers.
基金Supported by National Natural Science Foundation of China(Grant Nos.52075458 and U2141211).
文摘Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-graphene as lubricating additive, with the original graphene as a comparison. The physicochemical properties and lubrication performance of the as-prepared greases were evaluated in detail. The results show that the as-prepared greases have high dropping point and colloidal stability. Furthermore, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, spilled oil, and adhesive grease greatly improves the lubrication function of grease. This research paves the way for modulating high-performance lithium complex grease to reduce the friction and wear of movable machinery.
基金Supported by National Natural Science Foundation of China(Grant Nos.51335005,51321092)National Key Basic Research Program of China(973 Program,Grant No.2013CB934200)the Foundation for the Supervisor of Beijing Excellent Doctoral Dissertation(Grant No.20111000305)
文摘The performance of a lubricant largely depends on the additives it involves. However, currently used additives cause severe pollution if they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide（GO） consists of only C, H and O and thus is considered to be environmentally friendly. So the tribological properties of the few-layer GO sheet as an additive in hydrocarbon base oil are investigated systematically. It is found that, with the addition of GO sheets, both the coefficient of friction（COF） and wear are decreased and the working temperature range of the lubricant is expanded in the positive direction. Moreover, GO sheets has better performance under higher sliding speed and the optimized concentration of GO sheets is determined to be 0.5wt%. After rubbing, GO is detected on the wear scars through Raman spectroscopy. And it is believed that, during the rubbing, GO sheets adhere to the sliding surfaces, behaving like protective films and preventing the sliding surfaces from contacting with each other directly. This paper proves that the GO sheet is an effective lubricant additive, illuminates the lubrication mechanism, and provides some critical parameters for the practical application of GO sheets in lubrication.
基金supported by the National Natural Science Foundation of China (No. 52001028)the Education Commission of Chongqing Municipality (No. KJQN20210141)the Chongqing Science and Technology Commission (Nos. cstc2020jcyj-msxmX0544 and cstc2019jcyj-msxm X0510)
文摘Although graphene oxide(GO)has emerged as an excellent lubricant additive in water,there remain great challenges in their practical application due to high production costs.By taking into account the low cost and also its excellent tribological properties,it is likely that nano-SiO_(2)can be used as a lubricant additive to partially replace GO.Hence,this paper aims to explore the tribological properties of nano-SiO_(2)incorporated in GO nanofluids for partial GO replacement by investigating the friction coefficient and wear volume of the prepared SiO_(2)/GO hybrid nanofluids for magnesium alloy/steel sliding pairs.The experiments reveal that the SiO_(2)/GO hybrids retain low friction coefficients as compared to individual GO or SiO_(2)at all test conditions in this study.However,as for the bearing capacity test,all samples can provide a low wear volume under the loads of 1 and 3 N.With the increase of the normal load,there is considerable differences in the anti-wear behavior.Compared with that of individual GO nanofluids,the wear volume of the GO/SiO_(2)(mass ratio of 0.3:0.2)hybrid nanofluids was reduced by50.5%at 5 N and by 49.2%at 8 N.Furthermore,the wear volume of the GO/SiO_(2)(mass ratio of 0.3:0.2)hybrid nanofluids was reduced by46.3%under the rigorous conditions,as compared to individual GO nanofluids.The findings provide new insights into developing carbon nanomaterial-based hybrid nanofluids for magnesium alloy formation.
基金This work was supported by the National Basic Research Program of China （No.2010CB923300）, the National Natural Science Foundation of China （No.91127042 and No.21173205）, the Chinese Academy of Sciences （No.XDB01020000）, the FR- FCUC （No.WK2340000012）, the USTC-NSRL Joint Funds （No.KY2340000021）, and the National Under- graduate Innovative Training Program of Ministry of Education （No.201210358064）.
文摘We investigate the fluorescence quenching of Rhodamine 6G （R6G）, a well known laser dye with a high fluorescence quantum yield, by as-synthesized graphene oxide （GO） in aqueous solution, which is found to be rather efficient. By means of steady-state and time-resolved fluorescence spectroscopy combined with detailed analysis about the linear absorption vari- ation for this R6G-GO system, the pertinent quenching mechanism has been elucidated to be a combination of dynamic and static quenching. Possible ground-state complexes be- tween R6G and GO during the static quenching have also been suggested. Furthermore, the direction of photoindueed electron transfer between R6G and GO has been discussed.
基金financial support from the Strategic Priority Reasearch Program of Chinese Academy of Sciences(No.XDA09010104)National Natural Science Foundation of China(Nos.51525206,51521091,51372253 and U1401243)the MOST of China(Nos.2016YFB0100100 and 2014CB932402)
文摘Graphene is a promising conductive additive for the lithium-ion batteries(LIBs) and shows great potential especially with its fast development of the large scale fabrication technology. This work has explored the influence of the incorporation of graphenes prepared by three typical methods on the electrochemical performance of the LiCoO_2-based cathode focusing on the choice for the effective graphene as conductive additive for the cathode of LIBs. Through the comparison of the intrinsic characteristics of graphenes and the electrochemical performance of electrodes with graphene, it is found that graphene with low disorder degree and large size is not suitable for LiCoO_2 cathodes as conductive additive. Conversely, the graphene with oxygen functional groups, relatively low surface area and proper size displays much better electrochemical performance when it is used as conductive additive. This work also demonstrates the transmission mechanism for different graphenes as conductive additives in the LiCoO_2 materials, and further reveals that the conductivity of graphene is not the only factor as conductive additives, surface chemistry and sheet size of the graphene are also essential factors which greatly influence the electrochemical performance of electrode. In addition, when combined with Super P, only 1% graphene is enough to construct an efficient conductive network in the electrode. This study also gives a new sight on the practical application of graphene as conductive additive for high performance LIBs.
基金supported by the Ministry of Science and Technology of China (No.2016YFA0200602)the National Natural Science Foundation of China (No.21573211 and No.21633007)the Fundamental Research Funds for the Central Universities (No.WK2340000063)
文摘The fluorescence quenching of Rhodamine 6G （R6G） by graphene oxide （GO） was interrogated by R6G fluorescence measurements using a set of controlled GO samples with varied C/O ratios as the quencher. The carbonyl groups on the GO nanosheet turned to play a dominant role in quenching the R6G fluorescence. The quenching in the static regime can be described by the ＂sphere of action＂ model. The significant absorption of the R6G fluorescence by the ground-state complex formed between R6G and GO was identified to be responsible for the static quenching mechanisms in quenching. This work offers the R6G/GO system. insights into the fluorescence
