title: Degradation of phenolic compounds by laccase immobilized on carbon nanomaterials: diffusional limitation investigation.
abstract: Carbon nanoparticles are promising candidates for enzyme immobilization. We investigated enzyme loading and laccase activity on various carbon nanoparticles, fullerene (C60), multi-walled carbon nanotubes (MWNTs), oxidized-MWNTs (O-MWNTs), and graphene oxide (GO). The loading capacity was highest for O-MWNTs and lowest for C60. The activity of laccase on various nanomatrices using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTs) as a substrate decreased in the following order: GO>MWNTs>O-MWNTs>C60. We speculated that aggregation of the nanoparticles influenced enzyme loading and activity by reducing the available adsorption space and substrate accessibility. The nanoparticle-immobilized laccase was then used for removal of bisphenol and catechol substrates. Compared to free laccase, the immobilized enzymes had significantly reduced reaction rates. For example, the reaction rate of GO-laccase conjugated with bisphenol or catechol substrates was only 10.28% or 12.33%, respectively, of that of the free enzyme. Considering that there was no obvious structural change observed after enzyme immobilization, nanomatrix-induced diffusional limitation most likely caused the low reaction rates. These results demonstrate that the diffusional limitation induced by the aggregation of carbon nanoparticles cannot be ignored because it can lead to increased reaction times, low efficiency, and high economic costs. Furthermore, this problem is exacerbated when low concentrations of environmental contaminants are used.
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin 300071, China.
authors.forename: Ran
authors.initials: R
authors.lastname: Pang
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin 300071, China.
authors.forename: Mingzhu
authors.initials: M
authors.lastname: Li
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin 300071, China. Electronic address: zhangchengdong@nankai.edu.cn.
authors.forename: Chengdong
authors.initials: C
authors.lastname: Zhang
mesh_terms: D001559:Benzhydryl Compounds / Q000378:metabolism*; D052160:Benzothiazoles / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002244:Carbon / Q000737:chemistry*; D002396:Catechols / Q000737:chemistry / Q000378:metabolism; D004058:Diffusion; D004800:Enzymes, Immobilized / Q000737:chemistry / Q000378:metabolism*; D037741:Fullerenes / Q000737:chemistry / Q000378:metabolism; D006108:Graphite / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D042845:Laccase / Q000737:chemistry / Q000378:metabolism*; D049329:Nanostructures / Q000737:chemistry*; D037742:Nanotubes, Carbon; D010084:Oxidation-Reduction; D010636:Phenols / Q000378:metabolism*; D013451:Sulfonic Acids / Q000378:metabolism*; D000098826:Bisphenol A Compounds
chemical_list: D001559:Benzhydryl Compounds; D052160:Benzothiazoles; D002244:Carbon; D002396:Catechols; D004800:Enzymes, Immobilized; D037741:Fullerenes; D006108:Graphite; D042845:Laccase; D037742:Nanotubes, Carbon; D010636:Phenols; D013451:Sulfonic Acids; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; C034221:catechol; C006780:bisphenol A; D000098826:Bisphenol A Compounds; C069837:fullerene C60
keywords: Carbon nanoparticles; Degradation; Immobilization; Laccase; Phenolic compounds