Nanoparticles size distribution and phenol photodegradation with TiO2/C support obtained by phosphoric acid activation of palm kernel shell

https://doi.org/10.1016/j.micromeso.2019.02.012Get rights and content

Highlights

  • Activated carbon (AC) was prepared from Palm Kernel Shell by chemical activation with H3PO4.

  • The textural properties of the supports are important when these are used in photocatalytic processes.

  • The phenol photodegradation is increased until 14% in comparison with adsorption process.

Abstract

Activated carbon (AC)/TiO2 was prepared by infiltration of Degussa P25. The AC was obtained from palm kernel shell by chemical activation with H3PO4. The composite particle size is higher than TiO2 particles, because the TiO2 particles are distributed and immobilized on a porous support. The particles size distribution of TiO2 was found to be between 10.5 and 25 nm. The impregnation process introduced changes in the textural properties. As a result, the microporosity percentage was decreased, and the mesoporosity percentage was increased. The results were verified by different techniques such as: Scanning Electronic Microscopy (SEM), X-Ray Diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), and gas adsorption (N2 and CO2). For the textural properties, theoretical models were used such as Non-Local Density Functional (NLDFT) theory, fractal dimension, Dubinin-Radushkevich (DR), and Dubinin-Astakhov (DA) models. The AC has a positive effect in the phenol photodegradation process; that is, the degradation percentage is increased by 40% because of the synergic effect between components of the composite.

Introduction

Advanced oxidation processes are efficient methods for the removal of different organic pollutants present in surface and ground water. In these processes, photocatalysis has emerged as a potential methodology owing to total mineralization and the elimination of refractory pollutants even in low concentrations, thus decreasing the toxicity of water [1,2].

Titanium dioxide catalysts have been reported to be effective photocatalysts for the phenol photodegradation due to their optical and electrical properties, chemical stability and low cost. However, their particle size has been estimated to be in the order to 5–60 nm, which makes it more difficult to separate them from solution, especially in large-scale systems [3,4].

In a heterogeneous catalysis processes, carbonaceous material is used as adsorbents [5], catalytic supports [6], and even as catalysts by themselves [7]. Thus, different conventional forms have been used, such as carbon black, graphite, graphitized materials, and activated carbon. These have properties that make them interesting such as their stability in acid and basic medium, chemical surface groups, textural characteristics, and their adsorbent, mechanical, and electrical properties.

Recent research has found that there is an increase in the photocatalytic response of carbon/TiO2 systems owing to individual and collective factors associated with visible light absorption, textural parameters, and strong interfacial electronic effects. Some researchers have considered the use of AC as a photocatalytic support because it has a high surface area where the TiO2 particles can be distributed and immobilized [8,9].

In this way, a synergistic effect is observed between both phases in the processes of photodegradation which is justified by the weak interactions between the TiO2 and the support [10,11]. In other words, the photocatalytic activity is a function of the nature the catalyst and its ratio with carbonaceous matrix.

In fact, it has been found that the incorporation of a carbonaceous matrix has a positive effect not only on the activity, where it determines the reaction rate and pollutant-degradation efficiency, but also on the preferential mechanism that is followed in oxidation reactions and on the degree of mineralization attained in the reaction [11,12].

For this reason, this work involves finding solutions for preparing photocatalysts with a larger particle size that will allow the combination of textural, structural, and chemical properties to achieve better efficiency in the phenol photodegradation process.

In this research, the textural property changes of activated carbon obtained by chemical activation are evaluated and the effect of infiltration of Degussa P25 on its structure is determined. The composite should have a larger particle size than Degussa P25. In fact, this allows one to combine textural, chemical, and structural properties to improve efficiency in the photodegradation reaction of phenol.

Section snippets

Prepraration of AC

Palm kernel shells were selected as the raw material and these were obtained from Cesar, Colombia. The material was crushed and sieved to obtain particle sizes between 0.125 and 0.6 mm. The precursor, palm kernel shells, was impregnated with a solution of H3PO4 with a degree of impregnation of 0.60 g P/g of precursor. Phosphoric acid is a Brönsted acid and a strong dehydrating agent. Thus, the impregnation period was 2 h and the material was treated under a flow of nitrogen (80 mL/min) in a

Textural parameters

The textural parameters of the photocatalysts used in the degradation of phenol were determined by physisorption of N2 at 77 K. In Fig. 1, it is shows that as the percentage of titanium increases (AC-Ti 10% and AC-Ti 15%), there is also an increase in the surface area until it reaches 27.8%. However, the surface area decreases to 2.8% in comparison with the original parameters when the impregnation percentage is increased to 20%. The isotherms obtained are classified according to the IUPAC in

Conclusions

AC-Ti catalysts were prepared by infiltration of a suspension of Degussa p25 and applied to the removal of phenol from aqueous solution. This study allowed us to develop a method for the characterization of TiO2 nanoparticle distribution and size based on nitrogen isotherms at 77 K. In other hand, the impregnation affects the textural parameters due to the TiO2 blocking the microporosity but increasing the mesoporosity. The surface fractal dimension of photocatalysts varies from 2.96

Acknowledgements

The authors thank the Framework Agreement between the Universidad de los Andes, Colombia and the Universidad Nacional de Colombia and the act of agreement established between the Chemistry Departments of the two universities, under which this research was conducted. The authors also thanks the grant the funding assignment of resources destinated to the finalization of projects leading to the obtaining of a product of new knowledge 2018.

COLCIENCIAS, National Doctorates 2016 No. 757. Colombia

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