Facile Low-Temperature synthesis of novel carbon nitrides for efficient conversion of carbon dioxide into Value-Added chemicals.

The interest in using carbon nitrides (CN) for CO2 conversion has stimulated extensive research on CN synthesis. Herein, we report the synthesis of two novel CN materials using low-cost commercially available precursors at low temperatures in a short duration of time. Two CN materials, one derived from 5-amino tetrazole (named 4NZ-CN) and the other derived from 3, 5-diamino-1, 2, 4-triazole (named 3NZ-CN) precursors, are prepared by refluxing these precursors for 2 h at 100 °C. 4NZ-CN and 3NZ-CN catalysts show higher surface areas (55.80 and 52.00 m2 g-1) and more basic sites (10.05 and 5.65 mmol g-1) than the conventional graphitic carbon nitride (g-C3N4) derived from melamine, for which the corresponding values are 9.20 m2 g-1 and 0.62 mmol g-1, respectively. In addition, both CN exhibit a 3-fold higher catalytic activity for CO2 cycloaddition to epoxides than g-C3N4. The structure-activity relationship was ascertained using a combination of experimental and computational studies, and a catalytic mechanism was proposed. This work provides a facile strategy for the synthesis of novel CN materials at relatively low temperatures, and the developed catalysts show remarkable performance in the conversion of CO2 to value-added chemicals.

Zn-MOF as a Single Catalyst with Dual Lewis Acidic and Basic Reaction Sites for CO2 Fixation.

Continuous increase in carbon dioxide (CO2) emissions are causing imbalances in the environment, which impact biodiversity and human health. The conversion of CO2 to cyclic carbonates by means of metal-organic frameworks (MOFs) as a heterogeneous catalyst is a prominent strategy for rectifying this imbalance. Herein, we have developed nitrogen-rich Zn (II) based metal-organic framework, [Zn(CPMT)(bipy)]n (CPMT = 1-(4-carboxyphenyl)-5-mercapto-1H-tetrazole; bipy = 4,4'-bipyridine), synthesized via a mixed ligand strategy. This Zn-MOF showed high chemical stability in both acidic and basic conditions, and in organic solvents for a long time. On account of the concurrent presence of acid-base active sites and strong chemical stability under abrasive conditions, this Zn-MOF was employed as an effective catalyst for the coupling of CO2 and epoxides, under atmospheric pressure, mild temperature, and neat conditions. This Zn-MOF shows remarkable activity by producing high yields of epichlorohydrin carbonate (98%) and styrene carbonate (82%) at atmospheric CO2 pressure, 70 °C temperature, and 24 h reaction time, with turnover numbers (TON) of 217 and 181, respectively. The Zn-MOF could be reused for up to seven cycles with structural and framework integrity. Overall, this work demonstrates the synthesis of a novel and highly efficient MOF for CO2 conversion.