Metal-Free H2 Activation for Highly Selective Hydrogenation of Nitroaromatics Using Phosphorus-Doped Carbon Nanotubes.

We reported that phosphorus-doped carbon nanotubes (P-CNTs), showing metal-like properties, can efficiently promote metal-free hydrogenation of nitrobenzene (1a) to aniline (2a) using molecular hydrogen (H2) as a reducing reagent under very mild conditions with a reaction temperature of only 50 °C. The kinetics of 1a hydrogenation over P-CNT reveals that the hydrogenation rate of 1a is a first-order dependence on the H2 pressure and the P-CNT loading level, and a zero-order dependence on 1a concentration, demonstrating the rate-determining step of H2 adsorption and activation over P-CNT. The activation energy of P-CNT-catalyzed 1a hydrogenation is 43 ± 3 kJ mol-1 with the turnover frequency around 3.60 ± 0.12 h-1 at 50 °C. In addition to 1a, the general applicability of the P-CNT-promoted metal-free hydrogenation process is further demonstrated by applying various functionalized nitroaromatics with wide industrial interest. The P-CNT shows both excellent yields and selectivities to hydrogenation with respect to reducible, labile, and strong leaving groups on the nitroaromatics molecules. The stability and reusability of the P-CNT demonstrate up to eight-time recycling without evident loss of activity and selectivity. In addition to hydrogenation, metal-free catalytic transfer hydrogenation of 1a is achieved with P-CNT using diverse hydrogen sources, including hydrazine hydrate (N2H4·H2O), carbon monoxide/water (CO/H2O), and formic acid/triethylamine (HCOOH/Et3N).

Metal-Free N-Formylation of Amines with CO2 and Hydrosilane by Nitrogen-Doped Graphene Nanosheets.

N-Formylation of amines with carbon dioxide (CO2) as a carbonyl source is emerging as an important way for CO2 transformation into high-value-added chemicals; however, the developed catalytic systems mainly focused on transition-metal-based homogeneous catalysts. Herein, we reported rationally designed nitrogen-doped graphene nanosheets (NG) as metal-free catalysts for N-formylation of various amines with CO2 and hydrosilane to formamide under mild conditions. The NG catalyst displayed a wide amine scope with the desired formamide yields up to >99%, demonstrating its comparable catalytic performance to the reported transition-metal-based catalysts. Our experimental research reveals that the N-formylation of aniline involves an initial NG-promoted CO2 hydrosilylation with PhSiH3 to silyl formate and a subsequent nucleophilic attack of the aniline to give N-formanilide. Moreover, the key step of CO2 hydrosilylation can be simplified to a pseudo-first-order reaction under a high CO2 concentration with an observed reaction rate constant (kobs) of 226 h-1 at 40 °C and an apparent activation energy (Ea) of 34 kJ mol-1. In sharp contrast, a kobs of 23 h-1 and Ea of 47 kJ mol-1 were observed under catalyst-free conditions. Our theoretical investigation indicates that NG-promoted CO2 hydrosilylation corresponds to an exergonic reaction (ΔG = -0.53 eV), which is much lower in energy state than that of catalyst-free conditions (ΔG = -0.44 eV). Finally, the NG showed outstanding recyclability in the N-formylation reaction with almost unchanged catalytic performance during twelve-time recycling. This research thus represented a breakthrough in metal-free transformation of CO2 into fine chemicals with low-cost, environment-friendly, and carbon-based catalysts to replace the scarce and expensive transition-metal-based catalysts.

A colon targeted drug delivery system based on alginate modificated graphene oxide for colorectal liver metastasis.

A major problem associated with colon cancer is liver metastasis. A colon-targeted drug delivery system is one way to address this problem after the resection of colorectal cancer. However, traditional drug delivery systems face many challenges, such as an inability to control the release rate, inaccurate targeting, susceptibility to the microenvironment and poor stability. Here, we report the development of a graphene oxide (GO)-based, sodium alginate (ALG) functionalized colon-targeting drug delivery system, that is loaded with 5-fluorouracil (5-FU) as the anti-cancer drug (denoted as GO-ALG/5-FU). Our results demonstrate that the as-prepared drug delivery system possesses a much lower toxicity and better colon-targeting controlled-release behaviours. We show that GO-ALG/5-FU significantly inhibited tumour growth and liver metastasis and prolonged the survival time of mice. We anticipate that our assay will help improve basic research of colon-targeted drug delivery systems and provide a new way to treat colon cancer liver metastasis.