Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for Cu(II) Through Microwave Pre-Pyrolysis

Summary

Here, we present a protocol to synthesize nitrogen/oxygen dual-doped mesoporous carbon from biomass by chemical activation in different pyrolysis modes followed by modification. We demonstrate that the microwave pyrolysis benefits the subsequent modification process to simultaneously introduce more nitrogen and oxygen functional groups on the carbon.

Abstract

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is proposed. Bagasse impregnated with phosphoric acid is utilized as the precursor. To pyrolyze the precursor, two separate heating modes are used: microwave pyrolysis and conventional electric-heating pyrolysis. The resulting bagasse-derived carbon samples are modified with nitrification and reduction modification. Nitrogen (N)/oxygen (O) functional groups are simultaneously introduced to the surface of activated carbon, enhancing its adsorption of Cu(II) by complexing and ion-exchange. Characterization and copper adsorption experiments are performed to investigate the physicochemical properties of four prepared carbon samples and determine which heating method favors the subsequent modification for doping of N/O functional groups. In this technique, based on analyzing data of nitrogen adsorption, Fourier transform infrared spectroscopy, and batch adsorption experiments, it is proven that microwave-pyrolyzed carbon has more defect sites and, therefore, time-saving effective microwave pyrolysis contributes more N/O species to the carbon, although it leads to a lower specific surface area. This technique offers a promising route to synthesis adsorbents with higher nitrogen and oxygen content and a higher adsorption capacity of heavy-metal ions in wastewater remediation applications.

Introduction

Activated carbon has unique adsorption properties, such as a developed porous structure, a high specific surface area, and various surface functional groups; therefore, it is employed as an adsorbent in water treatment or purification^1,2,3,4. Besides its physical advantages, activated carbon is cost-effective and harmless to the environment, and its raw material (e.g., biomass) is abundant and easily obtained^5,6. The physicochemical properties of activated carbon depend on t....

Protocol

1. Preparation of Bagasse-based Activated Carbon

1. Preparation of the precursor for bagasse-based activated carbon
   1. Rinse the bagasse (obtained from a farm in Jiangsu, China) with deionized water and put the samples in a drying oven at 100 °C for 10 h.
   2. Crush the dried bagasse with a grinder and sieve the powder through a 50-mesh sieve.
   3. Place 30 g of fine bagasse powder into a 15 wt% phosphoric acid (H₃PO₄) solution in a 1:1 weight ratio for 24 h. Dry the mixture in an oven at 105 °C for 6 h. Collect the resulting product as the precursor for bagasse-based activated carbon ....

Results

Nitrogen adsorption/desorption isotherms of four samples are presented in Figure 1. All adsorption isotherms show a rapid increase in low P/P₀ region and these isotherms belong to type IV (IUPAC classification) demonstrating their pore structure that consists of micropores and dominant mesopores³².

The surface physical parameters for all samples obtained from the n.......

Discussion

In this protocol, one of the critical steps is the successful preparation of mesoporous carbon with better physicochemical properties by the one-step approach, where optimal experimental conditions need to be determined. So, in a previous study²⁸, we have carried out orthogonal array microwave pyrolysis experiments, considering the effect of the impregnation ratio of bagasse and phosphoric acid, pyrolysis time, microwave oven power, and drying time. Besides, great care must be taken in tedious Cu(.......

Materials

Name	Company	Catalog Number	Comments
All chemicals and reagents (phosphoric acid, etc.)	Nanjing Chemical Reagent Co., Ltd		Analytical grade
Electric furnace	Luoyang Bolaimaite Experiment Electric Furnace Co., Ltd
Microwave oven	Nanjing Yudian Automation Technology Co., Ltd		2.45 GHz frequency
Surface-area and porosimetry analyzer	Beijing Gold APP Instrument Co., Ltd		Vc-Sorb 2800TP
Fourier transform infrared (FTIR) spectrometer	Nicolet		6700
Flame atomic absorption spectrophotometry	Beijing Purkinje General Instrument Corporation		A3
Element Analyzer	Germany Heraeus Co.		CHN-O-RAPID