Use of carbon-based composites to enhance performance of TiO2 for the simultaneous removal of nitrates and organics from aqueous environments

Haruna Adamu (Corresponding Author), Mikaela Shand, Rebecca S F Taylor, Haresh G Manyar, James A Anderson

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The simultaneous photocatalytic removal of nitrate from aqueous environment in presence of organic hole scavenger using TiO2 has long been explored. However, the use of unmodified TiO2 in such reaction resulted in non-performance or release of significant amount of undesirable reaction products in the process, a problem that triggered surface modification of TiO2 for enhanced photocatalytic performance. Previous studies focused on decreasing rate of charge carrier recombination and absorption of light in the visible region. Yet, increasing active sites and adsorption capacity by combining TiO2 with a high surface area adsorbent such as activated carbon (AC) remains unexploited. This study reports the potential of such modification in simultaneous removal of nitrates and oxalic acid in aqueous environment. The adsorptive behaviour of nitrate and oxalic acid on TiO2 and TiO2/AC composites were studied. The Langmuir adsorption coefficient for nitrate was four times greater than that of oxalic acid. However, the amount of oxalic acid adsorbed was about 10 times greater than the amount of nitrate taken up. Despite this advantage, the materials did not appear to produce more active photocatalysts for the simultaneous degradation of nitrate and oxalic acid. The photocatalytic activity of TiO2 and its carbon-based composites was improved by combination with Cu2O particles. Consequently, 2.5 Cu2O/TiO2 exhibited the maximum photocatalytic performance with 57.6 and 99.8% removal of nitrate and oxalic acid, respectively, while selectivity stood at 45.7, 12.4 and 41.9% for NH4+, NO2- and N2, respectively. For the carbon based, 2.5 Cu2O/TiO2-20AC showed removal of 12.7% nitrate and 80.3% oxalic acid and achieved 21.6, 0 and 78.4% selectivity for NH4+, NO2- and N2, respectively. Using the optimal AC loading (20 wt%) resulted in significant decrease in the selectivity for NH4+ with no formation of NO2-, which unveils that selectivity for N2 and low/no selectivity for undesirable products can be manipulated by controlling the rate of consumption of oxalic acid. In contract, no nitrate reduction was observed with Cu2O promoted TiO2-T and its TiO2-(T)-20AC, which may be connected to amorphous nature of TiO2-T and perhaps served as charge carrier trapping sites that impeded activity.

Original languageEnglish
Pages (from-to)32001-32014
Number of pages14
JournalEnvironmental Science and Pollution Research
Volume25
Issue number32
Early online date13 Sep 2018
DOIs
Publication statusPublished - 30 Nov 2018

Fingerprint

Oxalic Acid
Oxalic acid
oxalic acid
Nitrates
Carbon
nitrate
carbon
Composite materials
Activated carbon
activated carbon
Charge carriers
Adsorption
adsorption
removal
scavenger
Photocatalysts
Contracts
Reaction products
Adsorbents
Genetic Recombination

Keywords

  • nitrate
  • oxalic acid
  • titania
  • activated carbon
  • composites
  • photocatalysis

Cite this

Use of carbon-based composites to enhance performance of TiO2 for the simultaneous removal of nitrates and organics from aqueous environments. / Adamu, Haruna (Corresponding Author); Shand, Mikaela; Taylor, Rebecca S F; Manyar, Haresh G; Anderson, James A.

In: Environmental Science and Pollution Research , Vol. 25, No. 32, 30.11.2018, p. 32001-32014.

Research output: Contribution to journalArticle

Adamu, Haruna ; Shand, Mikaela ; Taylor, Rebecca S F ; Manyar, Haresh G ; Anderson, James A. / Use of carbon-based composites to enhance performance of TiO2 for the simultaneous removal of nitrates and organics from aqueous environments. In: Environmental Science and Pollution Research . 2018 ; Vol. 25, No. 32. pp. 32001-32014.
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AU - Shand, Mikaela

AU - Taylor, Rebecca S F

AU - Manyar, Haresh G

AU - Anderson, James A

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N2 - The simultaneous photocatalytic removal of nitrate from aqueous environment in presence of organic hole scavenger using TiO2 has long been explored. However, the use of unmodified TiO2 in such reaction resulted in non-performance or release of significant amount of undesirable reaction products in the process, a problem that triggered surface modification of TiO2 for enhanced photocatalytic performance. Previous studies focused on decreasing rate of charge carrier recombination and absorption of light in the visible region. Yet, increasing active sites and adsorption capacity by combining TiO2 with a high surface area adsorbent such as activated carbon (AC) remains unexploited. This study reports the potential of such modification in simultaneous removal of nitrates and oxalic acid in aqueous environment. The adsorptive behaviour of nitrate and oxalic acid on TiO2 and TiO2/AC composites were studied. The Langmuir adsorption coefficient for nitrate was four times greater than that of oxalic acid. However, the amount of oxalic acid adsorbed was about 10 times greater than the amount of nitrate taken up. Despite this advantage, the materials did not appear to produce more active photocatalysts for the simultaneous degradation of nitrate and oxalic acid. The photocatalytic activity of TiO2 and its carbon-based composites was improved by combination with Cu2O particles. Consequently, 2.5 Cu2O/TiO2 exhibited the maximum photocatalytic performance with 57.6 and 99.8% removal of nitrate and oxalic acid, respectively, while selectivity stood at 45.7, 12.4 and 41.9% for NH4+, NO2- and N2, respectively. For the carbon based, 2.5 Cu2O/TiO2-20AC showed removal of 12.7% nitrate and 80.3% oxalic acid and achieved 21.6, 0 and 78.4% selectivity for NH4+, NO2- and N2, respectively. Using the optimal AC loading (20 wt%) resulted in significant decrease in the selectivity for NH4+ with no formation of NO2-, which unveils that selectivity for N2 and low/no selectivity for undesirable products can be manipulated by controlling the rate of consumption of oxalic acid. In contract, no nitrate reduction was observed with Cu2O promoted TiO2-T and its TiO2-(T)-20AC, which may be connected to amorphous nature of TiO2-T and perhaps served as charge carrier trapping sites that impeded activity.

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KW - titania

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