Elsevier

Chemosphere

Volume 306, November 2022, 135574
Chemosphere

Investigation of optimum Mn dopant level on TiO2 for dye degradation

https://doi.org/10.1016/j.chemosphere.2022.135574Get rights and content

Highlights

  • Mn–TiO2 was prepared employing sophisticated hydrothermal method.

  • 0.4 M Mn–TiO2-MG showed 96% efficiency on degrading MG dye.

  • 0.4 M Mn–TiO2-MG rate constant was higher than other samples.

  • 0.4 M Mn–TiO2 reaction system abide by Pseudo first order kinetics.

Abstract

Pristine and Mn–TiO2 photocatalysts was prepared employing sophisticated hydrothermal technique. TiO2, 0.2 M, 0.4 M Mn–TiO2 photocatalysts analysis were done by using standard characterization studies. The morphology of the pure TiO2 photocatalyst showed the large agglomeration of nanoparticles. While the dopant Mn ions influenced higher on host lattice TiO2. The 0.2 M Mn added TiO2 photocatalyst showed no agglomeration and nanoparticles size were decreased. On increasing dopant level, there is growth of nanorods along with nanoparticles which greatly helped in dye degradation. The prepared photocatalysts photocatalytic action was investigated on reducing MG dye. Prepared photocatalyst added dye mixtures were exposed under visible light and collected for every 15 min. 0.4 M Mn–TiO2- MG sample showed 96% efficiency on degrading MG dye. The dopant has increased electrons and holes recombination on host surface. 0.4 M Mn–TiO2-MG sample rate constant was higher than other samples and reaction system abide by Pseudo first order kinetics. 0.4 M Mn–TiO2 photocatalyst be an efficient and enthusiastic potential material to remove organic pollutants.

Introduction

Magnificent growth of industries was considered as the boon of nation which develops employment ratio and nation's GDP. On the contrary, most of the industries were not in control under government rules on discharging wastes. Number of industries is stuffing the hazardous effluents on to the water sources nearby without the knowledge of its side effects. The severe water demand was caused by 20% of sudden growth in population and 80% due to the inappropriate discharge of hazardous effluents. Industries like textiles, pharmaceuticals, cosmetics, food, leather and tannery, paper, plastics and clinical laboratories discharge wide range of perilous wastes on rivers, seas and ponds. By analyzing the polluted water, it contains dyes, heavy metals, pesticides, herbicides, dioxins etc., (Jo and Tayade, 2014). Malachite green (MG) is an organic dye with molar ratio of 364.911 g/mol. MG dye is broadly employed as biocide in aquaculture and it works against protozoan and fungal diseases. Malachite green is also used as ecto parasiticide. Additionally, MG dye is used as food colorant, additives for food products, dyeing agent in wool, leather, jute, cotton and also as a pesticide (Srivastava et al., 2004). MG dye is investigated and found to be carcinogenic and genotoxic in nature which harms humans and aquatics (Stammati et al., 2005). By the clarification on adverse effects, MG dye has been prohibited in many countries like U.S. however owing to its availability, performance and low cost it has been in market till today (Mittelstaedt et al., 2004).

Elimination of these pollutants is a highly challenging task. These chemicals have strong bonding that cannot be easily broke down with traditional methods. To eliminate the effluents with safer and precise method the long way research is going on. Advanced Oxidation Process (AOP) is regarded to be the best solution for water remediation (Liu and Zhao, 2000). AOP comprises of various methods like photolysis, ozonation, photocatalysis and Fenton process. On comparing all the methods, photocatalysis is the promising one for removal of organic compounds. The positives of photocatalytic process are it is cost effective method and it can mineralize large variety of organic materials. The dye degradation mechanism is purely based on electron–hole pair's creation and e and h+ pair's recombination. The transfer of electron starting valence to conduction produces holes in valence band. The produced units will react with H2O and O2 molecules present in the surface of photocatalyst and generate strong hydroxyl and superoxide radicals and the species will humiliate pollutants (Rauf and Ashraf, 2009).

With the betterment of the techniques different materials have been synthesized and investigated. Most of the materials revealed its potential on water remediation process. TiO2 is the well-known material regarded for photocatalytic process. TiO2 with its unique features can mineralize and degrade the organic pollutants. The superior activity possessed by TiO2 is purely depends on bandgap, crystal structure, porosity and surface hydroxyl population (Lee and Park, 2013). The pure TiO2bandgap is 3.2 eV equal to the UV light wavelength. By this bandgap, TiO2 meets up a greater hindrance on real time applications. When pure TiO2 is exposed to sunlight under photocatalytic reactions, the catalyst will absorb only 3% of sunlight which is equal to UV spectrum (Akpan and Hameed, 2009; Bonnet et al., 2015). The superior materials for doping with TiO2 will be the transition metals due to its filled ‘d’ orbital levels and inclusion of these materials on TiO2 will create other energy levels close by conduction level. This will be more useful during photocatalytic process (Khlyustova et al., 2020). The metal doping on TiO2 will efficiently reduce the bandgap or avert the recombination by electron hole trapping. Manganese (Mn) was chosen to be the dopant as it will enhance the phase transformation of TiO2 (Chauhan et al., 2012). The TiO2 nano powders can be produced via diverse methods similar to co-precipitation, sol-gel, hydrothermal route, biosynthesis and hydrolysis method (Sanchez-Martinez et al., 2018; Antonelli and Ying, 1995; Zhou et al., 2011; Raliya et al., 2015; Sun et al., 2010). Herein, we used hydrothermal route which is most widely reported as it can reduce agglomeration of nanostructures and the growth of crystals is highly defined. On surveying the reported literatures, the hydrothermal was stated to be the best one to adjust the electronic, structural and surface behavior of TiO2. The properties of TiO2 featured by optimized conditions will help in photocatalytic applications (Hidalgo et al., 2007).

Chen et al. (2007) bought TiO2 powder and degraded with 99% for 4 h (Chen et al., 2007). Jiangyan Yang et al. (2019) produced SiO2@TiO2 at emulsion surface and humiliated MG dye with 96% under UV light (Yang et al., 2019). Meghdad Pirsaheb et al. (2016) synthesized Ni doped TiO2 under mild hydrothermal conditions and degraded MG dye under sunlight and UV light and obtained 97% effectiveness (Pirsaheb et al., 2016). Jia et al. (2017) fabricated TiO2 by ball-milling method and degraded both Congo Red and Methylene Blue dye (Jia et al., 2017). HiralSoni et al. (2014) produced TiO2 by sol-gel route and reduced MG dye under UV light with 99% efficiency (Soni et al., 2014). Jaiswal et al. (2015) produced Cu and N–TiO2 by sol-gel method and degraded MB dye under 150 W Xenon lamps and achieved rate constant at 0.014 min−1 (Jaiswal et al., 2015). Tae- Ho Kim et al. (2013) produced Fe and N - doped TiO2 photocatalyst through sonochemical process which reduced the Indigo Carmine dye at 95% efficiency under solar simulator (Kim et al., 2013). Poonam Benjwal et al. (2015) fabricated Zn, Mn-doped TiO2using sol-gel method and reduced MB dye under UV light with 90% efficiency (Benjwal and Kar, 2015). In the present study, we reported Mn doped TiO2 via hydrothermal method. The products were further characterized. The prepared photocatalysts were utilized to reduce Malachite Green dye under visible light. Pure TiO2 sample possessed less efficiency whereas 0.4 M Mn doped TiO2 sample degraded the pollutant with complete efficiency. The 0.4 M Mn doped TiO2 photocatalyst achieved the rate constant of 0.031 min−1. Higher recombination rate developed by dopant in rutile TiO2 enhanced the photocatalytic activity and obtained higher efficiency in reducing the organic pollutants.

Section snippets

Experimental

Fig. 1 shows the experimental schema of the photocatalysts. Tert-n- Butyl- Orthotitanate (TNBT, 98%), Manganous chloride (MnCl2. 4H2O), and Malachite green (MG) dye was purchased from SRL Pvt. Ltd. Nitric acid (HNO3) was bought from Isochem laboratories Pvt. Ltd. Acetone, Whatmann paper, methanol were bought and distilled water used with an analytical grade. Experimental procedure was illustrated as follows. 0.8 M TNBT (8 ml) were dissolved in 40 ml DI water. 2 ml HNO3 were appended dropwise

Results and discussion

The pristine TiO2 XRD was illustrated with standard JCPDS card # 87–0920 with rutile tetragonal crystal system along with P42/mnm space group (Fig. 4) (Nwankwo et al., 2019). The 2θ values located at 27.4, 36.1, 41.3, 44.1, 54.5, 56.5, 62.8, 64.1, 69.01, and 70.01 was synchronized with hkl values of (110), (101), (111), (210), (211), (220), (002), (310), (301) and (112). The anatase phase of Mn doped TiO2 samples were in good agreement with JCPDS card # 78–2486 with body-centered tetragonal

Conclusions

Pure, 0.2 M and 0.4 M Mn doped TiO2 photocatalysts was flourishingly produced via hydrothermal technique. The synthesized photocatalysts behavior was analyzed employing XRD, UV, Pl, FT-IR, Raman and SEM. The pure TiO2 exhibited rutile phase and on further addition of Mn has attained the phase transition. The phase change of TiO2 greatly helped in photocatalytic process. The reduction in bandgap is due to the dopant (Mn) which gives the red shift and alters the bandgap. There is better growth of

Credit author statement

SP. Keerthana: Conceptualization, Writing – original draft, Writing – review & editing; R. Yuvakkumar: Writing – review & editing, Supervision, Resources; G. Ravi: Investigation, Writing – review & editing; Abdullah G. Al-Sehemi: Investigation, Formal analysis, Validation; Dhayalan Velauthapillai: Investigation, Formal analysis, Validation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by MHRD RUSA–Phase 2, UGC-SAP, DST-FIST, and PURSE grants. The Deanship of scientific research at King Khalid University is greatly appreciated for funding this work under grant no: R.G.P-2/62/43.

References (48)

  • Z. Jia et al.

    Strong enhancement on dye photocatalytic degradation by ball-milled TiO2: a study of cationic and anionic dyes

    J. Mater. Sci. Technol.

    (2017)
  • W.K. Jo et al.

    Recent developments in photocatalytic dye degradation upon irradiation with energy-efficient light emitting diodes

    Chin. J. Catal.

    (2014)
  • T.H. Kim et al.

    Synthesis of solar light responsive Fe, N co-doped TiO2 photocatalyst by sonochemical method

    Catal. Today

    (2013)
  • S.Y. Lee et al.

    TiO2 photocatalyst for water treatment applications

    J. Ind. Eng. Chem.

    (2013)
  • B. Liu et al.

    The structural and photoluminescence studies related to the surface of the TiO2 sol prepared by wet chemical method

    Mater. Sci. Eng., B

    (2006)
  • R.A. Mittelstaedt et al.

    Genotoxicity of malachite green and leucomalachite green in female Big Blue B6C3F1 mice

    Mutat. Res., Genet. Toxicol. Environ. Mutagen.

    (2004)
  • M. Muruganandham et al.

    Solar photocatalytic degradation of a reactive azo dye in TiO2-suspension

    Sol. Energy Mater. Sol. Cell.

    (2004)
  • U. Nwankwo et al.

    Synthesis and characterizations of rutile-TiO2 nanoparticles derived from chitin for potential photocatalytic applications

    Vacuum

    (2019)
  • P. Praveen et al.

    Sol–gel synthesis and characterization of pure and manganese doped TiO2 nanoparticles–A new NLO active material

    Spectrochim. Acta Mol. Biomol. Spectrosc.

    (2014)
  • M. Rajabi et al.

    Defect study of TiO2 nanorods grown by a hydrothermal method through photoluminescence spectroscopy

    J. Lumin.

    (2015)
  • R. Raliya et al.

    TiO2 nanoparticle biosynthesis and its physiological effect on mung bean (Vigna radiata L.)

    Biotechnol. Rep.

    (2015)
  • M.M. Rashad et al.

    The structural, optical, magnetic and photocatalytic properties of transition metal ions doped TiO2 nanoparticles

    J. Alloys Compd.

    (2013)
  • M.A. Rauf et al.

    Fundamental principles and application of heterogeneous photocatalytic degradation of dyes in solution

    Chem. Eng. J.

    (2009)
  • C.V. Reddy et al.

    Mn-doped ZrO2 nanoparticles prepared by a template-free method for electrochemical energy storage and abatement of dye degradation

    Ceram. Int.

    (2019)
  • Cited by (6)

    View full text