Quantification of Chemical States, Dissociation Constants and Contents of Oxygen-containing Groups on the Surface of Biochars Produced at Different Temperatures
- 2 December 2014
- journal article
- research article
- Published by American Chemical Society (ACS) in Environmental Science & Technology
- Vol. 49 (1), 309-317
- https://doi.org/10.1021/es5043468
Abstract
Surface functional groups such as carboxyl play a vital role in the environmental applications of biochar as a soil amendment. However, the quantification of oxygen-containing groups on a biochar surface still lacks systematical investigation. In this paper, we report an integrated method combining chemical and spectroscopic techniques that were established to quantitatively identify the chemical states, dissociation constants (pKa), and contents of oxygen-containing groups on dairy manure-derived biochars prepared at 100–700 °C. Unexpectedly, the dissociation pH of carboxyl groups on the biochar surface covered a wide range of pH values (pH 2–11), due to the varied structural microenvironments and chemical states. For low temperature biochars (≤350 °C), carboxyl existed not only as hydrogen-bonded carboxyl and unbonded carboxyl groups but also formed esters at the surface of biochars. The esters consumed OH– via saponification in the alkaline pH region and enhanced the dissolution of organic matter from biochars. For high temperature biochars (≥500 °C), esters came from carboxyl were almost eliminated via carbonization (ester pyrolysis), while lactones were developed. The surface density of carboxyl groups on biochars decreased sharply with the increase of the biochar-producing temperature, but the total contents of the surface carboxyls for different biochars were comparable (with a difference Ka ranges and the abundant contents of carboxyl groups on biochars is a prerequisite to recognition of the multifunctional applications and biogeochemical cycling of biochars.Keywords
Funding Information
- Ministry of Education of the People's Republic of China (J20130039)
- Ministry of Science and Technology of the People's Republic of China (2012AA06A203)
- National Natural Science Foundation of China (21277120, 2142500268, 41071210)
This publication has 36 references indexed in Scilit:
- In situ and ex situ spectroscopic monitoring of biochar's surface functional groupsJournal of Analytical and Applied Pyrolysis, 2013
- Abundant and Stable Char Residues in Soils: Implications for Soil Fertility and Carbon SequestrationEnvironmental Science & Technology, 2012
- Understanding Aqueous Dispersibility of Graphene Oxide and Reduced Graphene Oxide through pKa MeasurementsThe Journal of Physical Chemistry Letters, 2012
- Surface chemistry variations among a series of laboratory-produced biocharsGeoderma, 2011
- Influence of Pyrolysis Temperature on Biochar Property and Function as a Heavy Metal Sorbent in SoilJournal of Agricultural and Food Chemistry, 2011
- Characterization of Biochars Produced from Cornstovers for Soil AmendmentEnvironmental Science & Technology, 2010
- Transport and retention of biochar particles in porous media: effect of pH, ionic strength, and particle sizeEcohydrology, 2010
- Sustainable biochar to mitigate global climate changeNature Communications, 2010
- Surface Physical–Chemical Characteristics of Sludge ParticulatesWater Environment Research, 2000
- Strong-Acid, Carboxyl-Group Structures in Fulvic Acid from the Suwannee River, Georgia. 2. Major StructuresEnvironmental Science & Technology, 1995