Pd nano-catalyst supported on biowaste-derived porous nanofibrous carbon microspheres for efficient catalysis

Environmental pollution caused by the presence of aromatic aldehydes and dyes in wastewater is a serious global concern. An effective strategy for the removal of these pollutants is their catalytic conversion, possibly to valuable compounds. Therefore, the design of efficient, stable and long-lifetime catalysts is a worthwhile research goal. Herein, we used nanofibrous carbon microspheres (NCM) derived from the carbohydrate chitin present in seafood waste, and characterized by interconnected nanofibrous networks and N/O-containing groups, as carriers for the manufacture of a highly dispersed, efficient and stable Pd nano-catalyst (mean diameter ca. 2.52 nm). Importantly, the carbonised chitin’s graphitized structure, defect presence and large surface area could promote the transport of electrons between NCM and Pd, thereby endowing NCM supported Pd catalyst with high catalytic activity. The NCM supported Pd catalyst was employed in the degradation of some representative dyes and the chemoselective hydrogenation of aromatic aldehydes;this species exhibited excellent catalytic activity and stability, as well as applicability to a broad range of aromatic aldehydes, suggesting its potential use in green industrial catalysis.

Novel Non-Coplanar and Tertbutyl-Substituted Polyimides:Solubility,Optical,Thermal and Dielectric Properties

A novel aromatic diamine monomer bearing tertbutyl and 4-tertbutylphenyl groups,3,3'-ditertbutyl-4,4'-diaminodiphenyl-4''-tertbutylphenylmethane(TADBP),was prepared and characterized.A series of non-coplanar polyimides(PIs)were synthesized via a conventional one-step polycondensation from TADBP and various aromatic dianhydrides including pyromellitic dianhydride(PMDA),3,3',4,4'-biphenyltetracarboxylic dianhydride(BPDA),4,4'-oxydiphthalic anhydride(OPDA),3,3',4,4'-benzophenone tetracarboxylic dianhydride(BTDA)and 4,4'-(hexafluoroisopropylidene)dipthalic anhydride(6FDA).All PIs exhibit excellent solubility in common organic solvents such as N,N-dimethylformamide(DMF),N,N-dimethylacetamide(DMAc),N-methyl-2-pyrrolidone(NMP),dimethyl sulfoxide(DMSO),chloroform(CHCl3),tetrahydrofuran(THF),and so on.Furthermore,the obtained transparent,strong and flexible polyimide films present good thermal stability and outstanding optical properties.Their glass transition temperatures(Tgs)are in the range of 298 to 347℃,and 10%weight loss temperatures are in excess of 490℃with more than 53%char yield at 800℃in nitrogen.All the polyimides can be cast into transparent and flexible films with tensile strength of 80.5-101 MPa,elongation at break of 8.4%-10.5%,and Young's modulus of 2.3-2.8 GPa.Meanwhile,the PIs show the cutoff wavelengths of 302-356 nm,as well as low moisture absorption(0.30%-0.55%)and low dielectric constant(2.78-3.12 at 1 MHz).

Ultra-small Pd clusters supported by chitin nanowires as highly efficient catalysts

For the first time, chitin microspheres woven from nanowires with multi-scale porous structures were used as an excellent support for a catalyst of ultra-small Pd clusters. The Pd species anchored on the precursor Pre-Pd@chitin were 0.6 nm in average size, while the reduced catalyst Red-Pd@chitin featured ultra-small particles of 1.3 nm in average size. X-ray absorption spectroscopy （XAS） and transmission electron microscopy （TEM） demonstrated that the Pd catalyst in both oxidative and reductive states retained good dispersity and ultra-small clusters. The catalyst was tested for the hydrogenation of p-nitroanisole, exhibiting an excellent initial rate （13× that of commercial Pd/C） and excellent turnover frequency reaching 52,000 h^-1. Furthermore, the catalyst could be recycled and used more than 10 times with no decay of the catalytic activity, suggesting potential industrial applications.

Synthesis and Characterization of Fluorinated Polyimide Derived from 3,3＇-Diisopropyl-4,4＇-diaminodiphenyl- 3＂,4＂-difluorophenylmethane

A novel aromatic diamine monomer, 3,3＇-diisopropyl-4,4＇-diaminodiphenyl-3＂,4＂-difluorophenylmethane （PAFM）, was successfully synthesized by coupling of 2-isopropylaniline and 3,4-difluorobenzaldehyde. The aro- matic diamine was adopted to synthesize a series of fluorinated polyimides by polycondensation with various dian- hydrides： pyromellitic dianhydride （PMDA）, 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride （BPDA）, 4,4＇-oxydiph- thalic anhydride （ODPA） and 3,3＇,4,4＇-benzophenone tetracarboxylic dianhydride （BTDA） via the conventional one-step method. These polyimides presented excellent solubility in common organic solvents, such as N,N-dimeth- ylformamide （DMF）, N,N-dimethyl acetamide （DMAc）, dimethyl sulfoxide （DMSO）, N-methyl-2-pyrrolidone （NMP）, chloroform （CHC13）, tetrahydrofuran （THF） and so on. The glass transition temperatures （Tg） of fluorinated polyimides were in the range of 260--306 ℃ and the temperature at 10% weight loss in the range of 474--502 ℃ Their films showed the cut-off wavelengths of 330--361 nm and higher than 80% transparency in a wavelength range of 385--463 nm. Moreover, polymer films exhibited low dielectric properties in the range of 2.76--2.96 at 1 MHz, as well as prominent mechanical properties with tensile strengths of 66.7--97.4 MPa, a tensile modulus of 1.7--2.1 GPa and elongation at break of 7.2%- 12.9%. The polymer films also showed outstanding hydrophobicity with the contact angle in the range of 91.2°--97.9°.