Influence of surface chemistry of carbon materials on inorganic nitrogen contaminants chemisorption

Adsorption of inorganic nitrogen contaminants (INC), namely ammonium (NH4 +), nitrate (NO3-), and nitrite (NO2-), using carbon materials (CMs) such as activated carbon (AC), and biochar (BC) has been widely implemented. This study was based on the hypothesis that surface chemical properties of CMs significantly influence INC adsorption. A range of physicochemical characterizations of CMs was performed to correlate INC adsorption with CM's surface properties. NH4 + adsorption study was conducted using coconut shell and charcoal-based AC, and poultry litter (PL), enhanced poultry litter (EPL), and rice husk (RH) BCs. The study revealed that PL with the lowest surface area (3 m2 g-1) and largest pore diameter (29 nm) had the highest NH4 + adsorption capacity (0.34 mg NH4 + g-1). Charcoal-based AC, with the highest surface area (1133 m2 g-1) and small pore diameter (6 nm), had the least NH4 + adsorption capacity (0.09 mg NH4 + g-1). Carboxyl, carbonyl, and phenolic groups were the specific acidic surface functional groups (SFGs) that enhanced NH4 + chemisorption via electrostatic interaction (EI). Specific SFGs that control NH4 + adsorption regardless of the type of CM were confirmed for the first time. NO3- and NO2- chemisorption mechanisms on CMs were elucidated by studying unmodified AC, and six modified ACs, and PL, EPL, and RH BCs. Highest Langmuir adsorption capacities of 7.08 mg NO3- g-1, and 17.38 mg NO2- g-1 by acid modified AC (AC-S) and 2.65 mg NO3- g-1, and 2.81 mg NO2- g-1 by high-temperature modified AC (AC-1000) were observed. Protons of AC-S and π-electrons of AC-1000 enhanced NO3- and NO2- adsorption capacities (NNACs) via EI. The presence of oxygen-containing SFGs, high ash content, and elements like Si reduced NNACs. pHzpc of adsorbents was lower than equilibrium pH of the solutions i resulting in negative surface charge that further inhibited NNACs. EI was confirmed as the dominant chemisorption mechanism for both NO3- and NO2- by studying unmodified and surface modified ACs and BC adsorbents. Understanding the precise role of redox-reactive quinone SFG towards NO3- chemisorption was achieved by modifying the surface of AC using naphthoquinone (AC-NQ) and anthraquinone (AC-AQ). After modification, the surface quinone content increased to 2.17 and 1.71 % in ACNQ and AC-AQ, while there was no quinone content detected on unmodified AC. BET (Brunauer–Emmett–Teller) surface area of AC-NQ and AC-AQ reduced by 82 and 47 %, respectively, compared to unmodified AC. A simultaneous reduction in NO3- adsorption capacities by 53 and 21 % was observed in AC-NQ and AC-AQ samples compared to unmodified AC, respectively. AQ and NQ have interacted with AC surface via π-π interactions, blocking the active sites for NO3- chemisorption. For the first time, AC has been modified using AQ and NQ to study their influence towards NO3- chemisorption in aqueous media.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Civil Engineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2022

Author dc:creator

• Raj, Suma

Advisors dc:contributor.advisor

• Padhye, Lokesh P
• Sarmah, Ajit K

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/61067

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/61067