Post-synthesis plasma processing and activation of TiO2 photocatalyst for the removal of synthetic dyes from industrial wastewater

Abstract

In this study, TiO2 nanopowders were prepared by combining the surfactant assisted sol–gel method with microwave plasma calcination. Plasma calcination was performed just for 20–30 min for reducing the calcination time and ensuring the energy efficient synthesis of photocatalyst. The mixed anatase–rutile phased TiO2 nanoparticles were obtained under these synthesis conditions. The band gap energy of the photocatalyst decreased by 40% on microwave plasma calcination. The surfactants were found to be ineffective on phase transformations of synthesized TiO2. FTIR analysis confirmed the absorption of O–Ti–O band stretching between 415 and 420 cm−1. The hydroxyl bands (OH) were observed to be less stretched after plasma calcination. The conventionally calcined HA–Ti, NA–Ti and MS–Ti samples showed band gap energies of 5.09 eV, 4.88 eV and 5.06 eV, respectively. The band gap energy of plasma calcined MTHA–Ti, MTNNA–Ti and MTMS–Ti samples was calculated about 4.92 eV, 3.11 eV and 4.96 eV, respectively. The combined effect of photocatalyst, plasma reactive species and UV radiations promoted the degradation efficiency of the methylene blue dye. Under DC plasma jet exposure, the maximum degradation efficiency of 95% was achieved after 30 min of plasma exposure time. The catalyst retained about 93–95% degradation efficiency after five cycles of dye degradation.

Full text

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Applied Physics A (2021) 127:307
https://doi.org/10.1007/s00339-021-04467-z
Post‑synthesis plasma processing andactivation of TiO2 photocatalyst
fortheremoval ofsynthetic dyes fromindustrial wastewater
S.Shukrullah1· M.Ayyaz1· M.Y.Naz1· K.A.Ibrahim2· N.M.AbdEl‑Salam3· H.F.Mohamed4
Received: 18 January 2021 / Accepted: 25 March 2021 / Published online: 3 April 2021
© The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2021
Abstract
In this study, TiO2 nanopowders were prepared by combining the surfactant assisted sol–gel method with microwave plasma
calcination. Plasma calcination was performed just for 20–30min for reducing the calcination time and ensuring the energy
efficient synthesis of photocatalyst. The mixed anatase–rutile phased TiO2 nanoparticles were obtained under these synthesis
conditions. The band gap energy of the photocatalyst decreased by 40% on microwave plasma calcination. The surfactants
were found to be ineffective on phase transformations of synthesized TiO2. FTIR analysis confirmed the absorption of O–
Ti–O band stretching between 415 and 420 cm−1. The hydroxyl bands (OH) were observed to be less stretched after plasma
calcination. The conventionally calcined HA–Ti, NA–Ti and MS–Ti samples showed band gap energies of 5.09eV, 4.88eV
and 5.06eV, respectively. The band gap energy of plasma calcined MTHA–Ti, MTNNA–Ti and MTMS–Ti samples was
calculated about 4.92eV, 3.11eV and 4.96eV, respectively. The combined effect of photocatalyst, plasma reactive spe-
cies and UV radiations promoted the degradation efficiency of the methylene blue dye. Under DC plasma jet exposure, the
maximum degradation efficiency of 95% was achieved after 30min of plasma exposure time. The catalyst retained about
93–95% degradation efficiency after five cycles of dye degradation.
Keywords TiO2 nanoparticles· Sol–gel method· Microwave plasma calcination· Dye degradation
1 Introduction
Owing to unique optical properties, high thermal and chemi-
cal stability and low-level toxicity [1], TiO2 nanoparticles
are being used in photovoltaics, photocatalysis [2–5], dye-
sensitized solar cells [6, 7], self-cleaning surfaces [8, 9],
agriculture, anticorrosive and antimicrobial surfaces, air and
water treatments [10, 11], cosmetics, batteries, sensors and
treatment of cancer cells [12]. The much-reported use of
TiO2 nanoparticles as a photocatalyst material is referred
to its dominant n-type semiconductor character [13]. The
band gap energy of TiO2 nanoparticles is reported between
3.0 and 3.2eV, depending on crystallographic arrangement
of structural planes [14, 15]. Wang etal. [16] and Karami
etal. [17] revealed that photocatalytic activity of anatase
phase of TiO2 relies on shape, size, surface morphology and
active surface area of the nanoparticles. However, the band
gap of anatase phase is not considered idea for fabrication of
solar devices, which limits its applications within the visible
wavelength range.
It is possible to tailor specific structural and optical
properties of TiO2 by deliberately choosing and optimiz-
ing the method of synthesis. The methods of synthesis of
TiO2 nanostructures include solvothermal method, hydro-
thermal method, aerosol method, plasma-solution interac-
tion method, chemical vapor deposition, coprecipitation
method, sol–gel method, thermochemical reaction, micro-
wave assisted synthesis, electrochemical reactions, etc
[14–19]. In certain cases, sol–gel process is favored over
other approaches, especially for the low-cost processing
ceramics, glasses of nanomaterials. A typical sol–gel process
* M. Y. Naz
yasin603@yahoo.com
* N. M. AbdEl-Salam
nelsalam@kus.edu.sa
1 Department ofPhysics, University ofAgriculture,
Faisalabad38040, Pakistan
2 College ofEngineering, Muzahimiyah Branch, King Saud
University, Riyadh11451, SaudiArabia
3 Arriyadh Community College, King Saud University,
Arriyadh11437, SaudiArabia
4 Applied Medical Science Department, Community College,
King Saud University, Riyadh11001, SaudiArabia
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