Equilibrium Constant of Bromothymol Blue Literature Value at 0 Degres
Synthesis of strontium ferrite and its role in the removal of methyl orange, phenolphthalein and bromothymol blue from laboratory wastewater
Abstract
The presence of organic chemical pollutants such as methyl orange (MOIn), phenolphthalein (PhIn) and bromothymol blue (BBIn) in laboratory wastewater is a challenge which requires immediate attention. In response to this challenge, strontium ferrite (SrFe 2O4) was prepared via co-precipitation method as an adsorbent for the removal of these pollutants from laboratory wastewater. SrFe2O4 was characterized by Fourier Transform Infrared spectrometer (FTIR), X-ray Diffraction analysis (XRD), Energy Dispersive X-Ray Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). FTR, XRD and RDS results confirmed the identity of SrFe2O4. SEM shows particles of SrFe2O4 of different dimensions and shapes, that reveal the coexistence of both monocrystalline and polycrystalline particles. The adsorption of the contaminants from aqueous solutions on SrFe 2O4 was studied in a batch system. The results showed that the adsorption is affected by the initial contaminant concentration (1.00–5.00 mg L−1), adsorbent dosage (0.05–0.10 g), adsorption temperature (303–323 K), and pH (2.1–11.0). SrFe2O4 removes the pollutants from water with adsorption capacities (7.00–8.60 mg g−1) and percentage removals (70.00–86.00%) that compared favourably with other previously reported adsorbents. The removal of the pollutants by SrFe2O4 obeys the pseudo-first-order model which can be described by the Langmuir isotherm model. The Gibb's free energy change (∆Go) and enthalpy change (∆Ho ) for the sorption process were negative while the entropy change (∆S o) was found to be 0.205, 0.282 and -0.221 kJ mol−1K−1 for MOIn, PhIn and BBIn respectively. The adsorption mechanism was considered to occur via electrostatic interaction. Regeneration capacities expressed by SrFe 2O4 were above 70% even after the 12th regeneration cycle. The sorption process was further described in molecular terms using computational quantum mechanical modelling, density functional theory (DFT). The use of SrFe 2O4 for the treatment of raw laboratory wastewater is effective towards the removal of MOIn, PhIN and BBIn.
Introduction
Maintaining a good quality of laboratory wastewater is a challenge. Large amount of wastewater is generated in the laboratory mostly after practical sessions or research studies. As research activities increase, the generation of waste chemicals from laboratory activities increases as well. Washing of glassware after chemical reactions or other chemical processes introduces some of these chemicals into wastewater emanating from laboratories. Most of the common laboratory chemical wastes are organic pollutants with acute toxicity and could be carcinogenic in nature. Over time, the removal of some of these chemicals from laboratory wastewater has become difficult as most laboratories were not designed to cater for the removal of these chemicals. The presence of the chemicals may hamper the quality of water and when discharged into the environment they may have a negative impact on or alter the aquatic ecosystem reducing sunlight and oxygen penetration, thus affecting the quality of aquatic life [1]. Examples of such laboratory chemicals commonly used are methyl orange (MOIn), phenolphthalein (PhIn) and bromothymol blue (BBIn).
MOIn, PhIn and BBIn (see molecular structure in Fig. 1) are chemical pH indicators commonly used in the laboratories. They are often used as chemical indicators for routine undergraduate and postgraduate practical sessions as well as during classical method of analysis. After being used as pH indicators, they are washed off glassware as waste. However, some laboratories from developing countries, generate laboratory wastes that are not properly treated and when they get into the environment, they become toxic and persistent which may cause serious environmental threat [2]; unfortunately, they are stable to heat, biodegradation and light [3,4]. Therefore, laboratory wastewater contaminated with these chemicals needs to be treated in order to remove the contaminants before they are discharged into the environment or considered for other purposes. Developing an efficient technique for the removal of these water pollutants or contaminants at low concentration in laboratory wastewater is very important. However, most previous attentions were focused on the removal of dyes from industrial effluents [5], [6], [7] without taking much care of how to treat laboratory wastewater with pollutants that can bio-accumulate at low concentration, causing serious challenges.
Methods reported for the removal of organic pollutants in water includes physical, biological, photochemical and chemical processes [8]. The methods involve ozonation, coagulation, reverse osmosis, adsorption and flocculation [9,10]. Most of these methods suffer from limitations such as being difficult to set up, non-sustainable, expensive, generation of toxic side products and low reusability. Among the known methods, adsorption still remains the easiest to set up and it is an environmentally friendly method [11]. Although, most adsorbents are expensive and have low regeneration capacity or reusability [12], adsorption still remains a viable process that can be easily modified to overcome its limitation. Currently, developing a cheap material with high regeneration capacity as adsorbent for the removal of chemical organic pollutants in laboratory wastewater is paramount. Therefore, this work is focused on developing a cheap material that can be used as efficient adsorbent for addressing this need.
The use of metal nanoparticles is currently receiving a deep interest in adsorption process because of its unique physicochemical properties such as high surface reactivity, small particle size, large surface area to volume ratio, high stability; good mechanical strength and photothermal stability [13,14]. The high stability, large surface area to volume ratio and small particle size have been of great advantage for the use of metal nanoparticles, such as iron oxide nanoparticles, as an adsorbent for the removal of organic pollutants in water . Despite the unique properties possessed by iron oxide particles, they still suffer from the formation of aggregates due to its oxidation in air, this aggregation limits their capacity to excel as adsorbent for the removal of organic pollutants such as MOIn, PhIn and BBIn from water. However, it has been reported that the properties exhibited by metal nanoparticles can be improved by physical or chemical modification [15].
To address the limitation, this work proposes the inclusion of an alkaline earth metal (strontium) in iron oxide to form strontium ferrite (SrFe2O4) by using the coprecipitation method. The concept of coprecipitation is expected to reduce aggregation and further enhance the removal of pollutants (MOIn, PhIn and BBIn) from water. According to our knowledge, there are very scarce works on the use of SrFe2O4 as adsorbent published in the literature [16]. This work aims to synthesize SrFe2O4 and study its use for the removal of MOIn, PhIn and BBIn from water. SrFe2O4 was synthesized and used via a batch adsorption process for the removal of MOIn, PhIn and BBIn from water system. The effects of pollutant concentration, adsorbent dose, pH, and operating temperature were investigated to rationalize the efficiency of the adsorbent, SrFe2O4. The adsorbent was further used for the treatment of raw laboratory wastewater contaminated with MOIn, PhIn and BBIn. Also, desorption capacity measurements of SrFe2O4 were carried out to evaluate its viability and to gain insight into the possible recovery of pollutants after treatment. The sorption of MOIn, PhIn and BBIn by SrFe2O4 was further studied by DFT calculations to describe the sorption process in molecular terms.
Section snippets
Materials
Strontium (II) chloride hexahydrate (SrCl2.6H2O), iron (III) chloride hexahydrate (FeCl3.6H2O), NaOH, ethanol, HCl, MOIn, PhIn, BBIn and all other chemicals used in this study were purchased from Aldrich Chemical Co., England and are all ACS reagent grade. Adansonia digitata seed oil was obtained from a market in Ibadan, Oyo state, Nigeria. They were used without further purification.
Synthesis of SrFe2O4 particles
SrFe2O4 particles were synthesized from SrCl2.6H2O and FeCl3.6H2O. This was achieved by continuous magnetic
Synthesis of SrFe2O4 particles
The fatty acid composition of the Adansonia digitata seed oil used as capping agent in the synthesis of SrFe2O4 particles has been reported to contain C18:1 (36.55 %) and C18:2 (28.19 %) fatty acids as the dominant fatty acids [18].
The XRD result of SrFe2O4 is presented in Fig. 2a. The diffractogram shows a single-phase spinel structure with the most intense peak at 2θ = 31.82o having a plane spacing corresponding to (240) for the plane of SrFe2O4 particles [19]. Subsequent planes corresponding
Conclusion
SrFe2O4 was prepared by co-precipitation method, a simple chemical reaction route for the removal of MOIn, PhIn and BBIn from wastewater. The prepared SrFe2O4 was characterized using XRD, EDS, FTIR, and SEM. The FTIR spectrum presents peaks suggesting the synthesis of SrFe2O4 at 3385, 592 and 381 cm−1 which was confirmed by corresponding signals from the XRD and results. The SEM shows that particles of SrFe2O4 are different dimension and shapes, which further revealed the coexistence of both
CRediT authorship contribution statement
Adewale Adewuyi: Conceptualization, Formal analysis, Investigation, Writing – original draft, Writing – review & editing, Visualization. Claudio A. Gervasi: Investigation, Supervision, Writing – review & editing, Visualization. María V. Mirífico: Investigation, Formal analysis, Supervision, Writing – original draft, Writing – review & editing, Visualization.
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.
Acknowledgment
A. Adewuyi appreciate the support from TWAS-UNESSCO Associateship for the award of research visit, and also grateful to Research Institute of Theoretical and Applied Physical Chemistry (INIFTA), Argentina for the provision of research space, chemicals and analysis; C.A. Gervasi gratefully acknowledges the Buenos Aires Commission for Scientific and Technological Research (CICBA) as a staff member of this Institution, and M.V. Mirífico gratefully acknowledges the Consejo Nacional de
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