Ce-Doped Smart Adsorbentswith Photoresponsive Molecular Switches for Selective Adsorption and Efficient Desorption

Achieving efficient adsorption and desorption processes by controllably tuning the properties of adsorbents at different technical stages is extremely attractive.However,it is difficult for traditional adsorbents to reach the target because of their fixed active sites.Herein,we report on the fabrication of a smart adsorbent,which was achieved by introducing photoresponsive azobenzene derivatives with cis/trans isomers to Ce-doped mesoporous silica.These photoresponsive groups serve as “molecular switches”by sheltering and exposing active sites,leading to efficient adsorption and desorption.Ce is also doped to provide additional active sites in order to enhance the adsorption performance.The results show that the cis isomers effectively shelter the active sites,leading to the selective adsorption of methylene blue(MB)over brilliant blue(BB),while the trans isomers completely expose the active sites,resulting in the convenient release of the adsorbates.Both selective adsorption and efficient desorption can be realized controllably by these smart adsorbents through photostimulation.Moreover,the performance of the obtained materials is well maintained after five cycles.

Fabrication of azobenzene-functionalized porous polymers for selective CO_(2) capture

Many solid adsorbents have been prepared for the CO_(2)capture.In particular,the photoresponsive adsorbents have attracted extensive interests because of their tunable pore structure and variable responsive behaviors provoked by the external light.However,it is challenging to fabricate the photoresponsive adsorbents featured the big CO_(2)capacity and high CO_(2)selectivity.Herein,copolymerized between 4-phenylazobenzoyl chloride,2,4,6-trichloro-1,3,5-triazine and melamine,a series of azobenzenefunctionalized porous polymers(PTM-AZOs)are successfully synthesized.The PTM-AZOs are verified in possession of proper pore structures,large surface area and photoconductive properties through a series of characterization.The PTM-AZO-2 with the trans-isomerization exhibits the best CO_(2)adsorption amount of 2.7 mmol·g^(-1)(273 K and 0.1 MPa),while the CO_(2)/N_(2)selectivity can reach 2459 and 607 on the trans-and cis-isomerization,respectively.The regulatable pore structures controlled by the photoresponsive azobenzene groups affect the CO_(2)capture performance of the PTM-AZOs.

Implementing an“Impracticable”Copolymerization to Fabricate a Desired Polymer Precursor for N-doped Porous Carbons

It is common that a proof-of-concept of a desired reaction,which might generate materials with new functions or application potential,is eventually proved impracticable or commercially unfeasible.Considerable efforts have been made but wasted in searching for unknown reaction conditions in solvent environments because it was believed that the activity of reactants can be enhanced to facilitate reactions by dissolving them in solvents.However,an abnormal case was discovered in this study.A desired copolymerization reaction between 1,3,5-tris(chloromethyl)-2,4,6-trimethylbenzene and melamine was confirmed to be impracticable under various solvent conditions;however,it was successfully implemented using a solvent-free method.Using first-principle calculations and molecular dynamics simulations,two decisive factors that the reaction in solvents cannot possess,namely the reaction equilibrium being pushed by the timely release of by-products and the confined thermal motions of the activated monomer molecules in the solid phase,were demonstrated to make the copolymerization successful in the solvent-free method.Owing to the high aromaticity and azacyclo-content,the as-synthetic copolymer exhibited good application potential as a precursor to fabricate N-doped porous carbons with satisfactory carbon yields,ideal N contents,desired textural properties,and competitive CO_(2)capture abilities compared to other representative counterparts reported recently.

Graphene-anchored sodium single atoms:A highly active and stable catalyst for transesterification reaction

Solid strong base catalysts have received considerable attention in various organic reactions due to their facile separation,neglectable corrosion,and environmental friendliness.Although great progress has been made in the preparation of solid strong base catalysts,it is still challenging to avoid basic sites aggregation on support and active sites loss in reaction system.Here,we report a tandem redox strategy to prepare Na single atoms on graphene,producing a new kind of solid strong base catalyst(Na1/G).The base precursor NaNO_(3)was first reduced to Na2O by graphene(400℃)and successively to single atoms Na anchored on the graphene vacancies(800℃).Owing to the atomically dispersed of basicity,the resultant catalyst presents high activity toward the transesterification of methanol and ethylene carbonate to synthesize dimethyl carbonate(turnover frequency(TOF)value:125.7 h^(−1)),which is much better than the conventional counterpart Na2O/G and various reported solid strong bases(TOF:1.0-90.1 h^(−1)).Furthermore,thanks to the basicity anchored on graphene,the Na1/G catalyst shows excellent durability during cycling.This work may provide a new direction for the development of solid strong base catalysts.

Photo-switchable Cu^(+)sites in metal-organic frameworks for adsorptive desulfurization

Photo-switchable metal-organic frameworks(PMOFs)as energy-saving adsorbents for tailorable guest capture show admirable potentials for various applications like adsorptive desulfurization.However,the regulation behavior of most reported PMOFs is based on weak physical interaction,and it is highly desired to introduce specific active sites to satisfy the demand of higher adsorption capacity and selectivity.Herein,for the first time,we prepared the PMOFs,azobenzene-functionalized HKUST-1(HK-Azo),simultaneously decorated with Cu_(2)O active sites that possess strong interaction with guest molecules.Due toπ-complexation interaction of Cu^(+)with aromatic sulfur compounds,the obtained HK-Azo shows obviously higher adsorption capacity on benzothiophene compared with HKUST-1.Upon ultraviolet(UV)and visible irradiation,azobenzene moieties in the PMOFs can transform their configuration freely and reversibly.Such trans/cis isomerization of azobenzene causes exposure/shelter of Cu_(2)O active sites,leading to controllable benzothiophene capture.The HK-Azo exhibits the change of benzothiophene uptake up to 29.7%upon trans and cis isomerization,which is obviously higher than HKUST-1 with negligible change.This work may inspire the development of new adsorption process regulated by light for adsorptive desulfurization that is impossible to realize by conventional PMOFs.

用于CO2捕获的智能吸附剂:促使强吸附活性位响应于可见光

基于光响应吸附剂的吸附过程可控性好、能源效率高,其在CO2捕获中的应用受到关注.然而,大多数报道的光响应吸附剂是基于弱吸附位点设计的,通过其结构或位阻的变化控制CO2吸附.此外,还需要用到紫外光来调节吸附能力.本文首次报道了用于CO2捕获的智能吸附剂,促使强吸附活性位响应于可见光.吸附剂的制备通过将伯胺和分散红(DR1,一种响应于可见光的推-拉型偶氮苯)引入介孔氧化硅实现.伯胺作为强吸附位点促使吸附剂对CO2的选择性高于CH4,而DR1则作为控制开关.光照前偶氮苯处于反式构型,降低了伯胺的电势,因而实现了吸附位点的暴露和CO2的自由吸附.偶氮苯在可见光的照射下转变为顺式结构,伯胺的电势提高,因而活性位点被遮蔽.即使是强吸附位点,吸附剂在光照前后对CO2的吸附量变化也可以达到40%.此外,DR1的反式/顺式异构可以通过可见光的控制实现可逆转变.本文报道的智能系统赋予了吸附剂选择性且避免使用紫外光,这对于传统吸附剂而言是难以实现的.

Breathing Metal-Organic Polyhedra Controlled by Light for Carbon Dioxide Capture and Liberation

Metal-organic polyhedra(MOPs)have emerged as versatile platforms for artificial models of biological systems due to their discrete structure and modular nature.However,the design and fabrication of MOPs with special functionality for mimicking biological processes are challenging.Inspired by the breathing mechanism of lungs,we developed a new type of MOP(a breathing MOP,denoted as NUT-101)by directly using azobenzene units as the pillars of the polyhedra to coordinate with Zr-based metal clusters.In addition to considerable thermal and chemical stability,the obtained MOP exhibits photocontrollable breathing behavior.Upon irradiation with visible or UV light,the configuration of azobenzene units transforms,leading to reversible expansion or contraction of the cages and,correspondingly,capture or liberation of CO_(2)molecules.Such a breathing behavior of NUT-101 is further confirmed by density functional theory(DFT)calculation.This system might establish an avenue for the construction of new materials with particular functionality that mimic biological processes.

An antiempirical strategy:sacrificing aromatic moieties in the polymer precursor for improving the properties of the derived N-doped porous carbons

With the carbonization at an elevated temperature,high aromaticity of a precursor for porous carbons was traditionally thought to be crucial for the resultant perfect textural properties and ideal application performances of the porous carbons.Thus,many efforts have been done to search or to artificially prepare the polymer precursors with higher aromaticity to generate more satisfying porous carbons.However,an antiempirical case was found in this study.The copolymerization between 1,3,5-tris(chloromethyl)-2,4,6-trimethylbenzene(TCM)and cyclohexane-1,4-diamine was successfully implemented to get a polymer code-named NUT-40,in which half of the ring structures are nonaromatic,while N-doped porous carbons(NDPCs)with better textural properties(e.g.,SBET=1363 m^(2)g^(-1)for NDPC-600)and competitive CO_(2)capture abilities(e.g.,CO_(2)capacity=4.3 mmol g^(-1)at 25℃and 1 bar for NDPC-600)were generated from the NUT-40,compared with the NDPC counterparts derived from the NUT-4 in a previous study(e.g.,SBET=958 m^(2)g^(-1)and CO_(2)capacity=3.8 mmol g^(-1)at 25℃and 1 bar for NDPC-600),in which TCM and ursol were employed as the monomers instead,and thus the ring structures in the NUT-4 was fully aromatic.With first-principle and molecular dynamics simulations,it was demonstrated that the embryo pore structure in the NUT-40 molecule can be more easily maintained during the carbonization than that of the NUT-4,which finally improves the surface area and porosity of the NUT-40 generated NDPCs.