Assessment of Reaction Parameters in the Polymeric Carbon Nitride Thermal Synthesis and the Influence in Photocatalytic Hydrogen Production

Dalila Monteiro,Marcus Vinicius Silva,Luciana Silva

doi:10.21577/0103-5053.20190251

Abstract

In this work, the reaction parameters for polymeric carbon nitride synthesis by thermal polycondensation were assessed, such as type of precursor, heating rate and time of thermal treatment, in order to obtain crystalline materials with high photocatalytic performance. All synthesized materials were tested as photocatalysts in hydrogen production using ethylenediaminetetraacetic acid (EDTA) as a sacrificial reactant under visible light irradiation (λ ≥ 420 nm). The synthesis condition capable to obtain the material that reached the best performance in photocatalytic hydrogen production was using thiourea as the precursor, due to the band gap narrowing and charge recombination suppression; an intermediate heating rate (5 oC min-1) and a longer thermal treatment time (6 h) that yielded a better crystalline solid. The combination of these effects led the S-doped polymeric carbon nitride (SPCN4 sample) to a higher photocatalytic activity, reaching the maximum hydrogen production rate of 214.75 µmol g-1 h-1.

Highlights

In the last decade, a lot of attention was devoted to study carbon nitride-based materials, nontoxic metal‐free photocatalysts that exhibit a great potential for photocatalytic hydrogen evolution
There is no consensus about the time of thermal treatment, which varies from 4 to 6 h, and the heating rate to reach 550 oC, that varies from 2 to 10 oC min-1.5-14 In general, the physical chemistry properties of polymeric carbon nitride (PCN) are related to the reaction parameters used in the synthesis, which will affect the photocatalytic activity of this material
The more intense one is indexed to the diffraction plane (002) and another one with low intensity is indexed to the diffraction plane (100) according to Joint Committee on Powder Diffraction Standards (JCPDS 87-1526). These results indicate that the polymeric structure is formed in all evaluated conditions; the diffractograms of the materials synthesized from thiourea (SPCN samples) present more intense peaks than those synthesized from urea (PCN samples), which suggests that thiourea as precursor induces a better crystallinity

Summary

Introduction

A lot of attention was devoted to study carbon nitride-based materials, nontoxic metal‐free photocatalysts that exhibit a great potential for photocatalytic hydrogen evolution. There is no consensus about the time of thermal treatment, which varies from 4 to 6 h, and the heating rate to reach 550 oC, that varies from 2 to 10 oC min-1.5-14 In general, the physical chemistry properties of PCN are related to the reaction parameters used in the synthesis, which will affect the photocatalytic activity of this material.

Results

Conclusion