Grantee Research Project Results
Final Report: Synthesis of Graphene Oxide/Magnesium Oxide Nanoparticles and Its Application for Removal of Emerging Contaminants in Drinking Water
EPA Grant Number: SU836141Title: Synthesis of Graphene Oxide/Magnesium Oxide Nanoparticles and Its Application for Removal of Emerging Contaminants in Drinking Water
Investigators: Sengor, S. Sevinc
Institution: Southern Methodist University
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
Various emerging contaminants are being discovered in water supplies that have detrimental effects on humans, endangering the long term sustainability of drinking water supplies. Endocrine disrupting chemicals (EDCs) and pharmaceuticals represent two classes of emerging organic contaminants that are ubiquitously present in municipal wastewater effluents. Endocrine disruptors are synthetic chemicals and natural plant compounds that may affect the endocrine system—the communication system of glands, hormones, and cellular receptors that control the body’s internal functions. Wastewater treatment plants are designed to remove conventional pollutants, such as suspended solids and biodegradable organic compounds, but they are not designed to remove low concentrations of emerging organic contaminants. The use and disposal of pharmaceuticals entering river and sewer systems can lead to EDCs. This may be related to the growing number of antibiotics, painkillers, and antidepressants in the population. The removal of these compounds in water is extremely critical from a sustainability viewpoint as this would provide a highly effective solution for enhancing the water quality for future generations.
The overall P3 proposal focuses on (i) development of a novel and cost-effective graphene based nanocomposite material for the efficient removal of emerging contaminants in water; (ii) provide opportunities for students and communities to learn about the new emerging contaminants such as EDCs discovered in water supplies; and (iii) optimize next generation water treatment technologies for sustainable drinking water sources, addressing the three components of sustainability: people, prosperity and the planet. The P3 project is intended to be developed and designed by interdisciplinary student team members in order to ultimately benefit people by improving the water quality, promoting prosperity, and protecting the planet by conserving water resources, minimizing water pollution in the most cost-effective way.
The objective of Phase I of the P3 project was to synthesize a novel graphene based material, Graphene Oxide/Magnesium(Hydr)Oxide nanocomposite (GO/Mg(hydr)oxide NC), and demonstrate its application for the removal of organic contaminants, such as EDCs, in water. Adsorption is one of the easiest and cheapest removal processes in water treatment. Graphene, one of the most fascinating advanced carbon-based materials is a promising material to be used for this purpose, as it has extraordinary characteristics such as large theoretical surface area and good chemical stability. Graphene Oxide (GO), oxidized derivative of graphene, contains functional groups, which results it to be easily dispersed in aqueous solutions. However, separation of GO from water is a challenging issue after treatment. Several catalyst materials have been developed and examined in the recent decade to be combined with GO to overcome this problem. Magnesium oxide is a low cost alkaline earth metal oxide with high surface reactivity and high adsorption capacity. It has recently been used for the removal of various organic pollutants from water and wastewater. In Phase I of the P3 project, we showed that GO/Mg(hydr)oxide is a successful composition to render the GO to be easily settled in aqueous solutions and it can be used for the successful removal of organic contaminants.
Summary/Accomplishments (Outputs/Outcomes):
The research objectives have been accomplished through laboratory batch experiments. The proposed work has been carried out by conducting the following tasks:
- Synthesis of Graphene Oxide (GO) materials
- Synthesis of Magnesium oxide (MgO) nanoparticles
- Synthesis of GO/Mg(hydr)oxide nanocomposite materials
- Perform laboratory batch experiments with selected endocrine disruptor compounds and GO/Mg(hydr)oxide NC materials to identify the optimum GO/Mg(hydr)oxide dosage, pH and contact time for best removal efficiency of the endocrine disruptor compound concentrations.
First, the Graphene Oxide (GO) materials have been synthesized using graphite powder (Task 1). Then the Magnesium oxide (MgO) nanoparticles were synthesized (Task 2). GO/Mg(hydr)oxide NC material was then synthesized using the GO and MgO nanoparticles (Task 3). Then the NC material was tested to analyze the best removal efficiency of an organic dye, methylene blue (MB) and a selected EDC compound, bisphenol A (BPA) (Task 4). The optimum NC dosage, pH and contact time for the best removal efficiency of these contaminants were identified using adsorption studies.
Effect of GO/Mg(hydr)oxide dosage. The effect of GO/Mg(hydr)oxide dosage (0.025-0.6 g/L) on the removal of BPA (50 mg/L) was studied at a pH of 7. The remaining BPA concentration was measured after 30 minutes of stirring the suspension on the magnetic stirrer. The results showed that the efficiency of adsorption increased by the increase of GO/Mg(hydr)oxide NCs dosage, which is due to the increase in the availability of adsorbent surface area and active sites provided at higher dosage. Based on the results, optimum adsorbent dosage for adsorbing 50 mg/L of BPA was chosen as 0.2 g/L and was used in the following experiments.
Effect of contact time. The effect of contact time on the adsorption of BPA on GO/Mg(hydr)oxide NC was investigated in the range of 2-60 minutes for the removal of 50 mg/L BPA concentration at pH 7. Figure 4 shows that the adsorption of BPA and MB onto GO/Mg(hydr)oxide NC took place rapidly in the first 5 minutes, then increased slowly. More than 84% of the BPA & MB was removed in the first two minute for which could be due to the high number of available adsorption sites at the beginning of the adsorption process, which then later became saturated. Hence, 5 minute contact time was chosen as the optimum time for the removal of BPA & MB onto GO/Mg(hydr)oxide.
Effect of pH. The effect of pH on the adsorption of BPA & MB onto GO/Mg(hydr)oxide NC was investigated in the range of 3-11 for the removal of 50 mg/L BPA concentration in 60 minutes. Our results showed that the efficiency of adsorption of BPA was dependent on the pH of the solution. According to the results, the highest and the lowest adsorption capacity of the BPA with GO/Mg(hydr)oxide NCs belong to pH 3 and pH 11, respectively. For better understanding of the pH effect, the pH of point of zero charge (pHpzc) of GO/Mg(hydr)oxide NCs was determined according to the pH drift procedure, where the pHpzc for GO/Mg(hydr)oxide ratios 5:1, 1:1, and 1:5 were determined to be ̴ 9.7, 10.5, and 10.5, respectively. At pH below pHpzc, the GO/Mg(hydr)oxide NCs surface has a positive charge and at pH above pHpzc the surface has a negative charge. Therefore, electrostatic attraction can be the dominant mechanism of adsorption between GO/Mg(hydr)oxide NCs and BPA when pH is below pHpzc. For pH values above pHpzc, other adsorption mechanisms such as hydrogen bonding and π−π interaction may attribute to the adsorption. For MB, electrostatic attraction can be the dominant mechanism of adsorption for pH above pHpzc. For pH values below pHpzc, other adsorption mechanisms, again such as hydrogen bonding and π−π interaction, may attribute to the adsorption.
Adsorption isotherms. Adsorption isotherms were studied to determine the adsorption mechanism using Langmuir and Freundlich models. Table 1 shows the parameters of Langmuir and Freundlich adsorption isotherms for MB and BPA adsorption onto GO/Mg(hydr)oxide NCs. As seen from Table 1, the correlation coefficients (R2) of the Langmuir isotherms are greater than the ones calculated by Freundlich isotherms for all ratios, indicating that the adsorption of MB ad BPA onto GO/Mg(hydr)oxide NCs would take place in a monolayer adsorption. The maximum adsorption capacity, qm, of BPA and MB onto GO/Mg(hydr)oxide NCs is 119 mg/g and 833 mg/g, respectively, based on the Langmuir isotherm (See Table 1).
[Insert Table 1]
A comparative summary of the adsorption capacity (qe) (mg/g) of GO/Mg(Hydr)oxide NC material to activated carbon (AC), as well as other graphene base powders for the removal of MB is provided in Table 2. It is seen that the adsorption capacity of the GO/Mg(hydr)oxide NC synthesized with the 5:1 ratio tested in this study is significantly higher (833 mg/g) compared to AC, PAC, GAC, as well as other GO based materials reported for MB removal so far. This high adsorption capacity shows that GO/Mg(hydr)oxide NCs are promising and applicable adsorbents for the removal of MB from wastewaters. As there are no toxicity standards set for EDCs yet, the removal efficiency of activated carbon can be used as a benchmark removal efficiency for the study. Activated carbon can remove 25% to 95% of different kinds of EDCs (Snyder et al., 2007). Therefore, the successful removal efficiency for the proposed process would be expected to be much higher for the EDCs.
[Insert Table 2]
The results showed that although the adsorption capacity of MB onto the NC was significantly high with 833 mg/g, the adsorption capacity of BPA was not as high as expected (119 mg/g). This could be due to the anionic structure of the BPA, compared to the cationic MB dye. Therefore, the first task of Phase II project will be to determine the specific characteristics that influence the adsorption of organic solutes onto the NC with particular emphasis being the strength of chemical bonds between the compound and the adsorbent. Several EDCs and other organic contaminants will be selected based on solute charge and hydrophobicity to be tested for this purpose. The high adsorption capacity of MB onto the NC (833 mg/g) will be used as a benchmark for the selected EDCs. The positive findings obtained, especially for MB sorption, warrant further investigation of the efficient removal of EDCs in solution using the synthesized NC. In Phase I, the synthesized GO/Mg(Hydr)oxide NC materials are also shown to be easily separated from solution by sedimentation, compared other graphene based composites reported by others (magnetic GO NCs), which would be significantly more costly to separate from solution through the requirements of magnetic field. A comparison of technical and economic feasibility of our NC adsorbent to others is summarized in Table 3. Our results indicate a high potential for the proposed technology to be transferred and adapted at any water treatment plant unit with a long term viability. The proposed technology would thus benefit the end users and the society through consuming clean, reliable drinking water.
[Insert Table 3]
Conclusions:
Graphene Oxide/Magnesium(hydr)oxide NC materials are synthesized and its application for the successful removal of MB dye as well as BPA from aqueous solutions is demonstrated. The efficiency of adsorption is observed to increase by the increase of GO/Mg(hydr)oxide NC dosage. The NCs have higher adsorption capacity than any of other graphene-based composite materials reported so far (833 mg/g for 5:1 ratio, based on Langmuir adsorption model). Almost all of MB concentrations tested in the range of 5-100 mg/L were removed in 20 minutes. In Phase I, the synthesized GO/Mg(Hydr)oxide NC materials are also shown to be easily separated from solution by sedimentation, compared other graphene based composites reported by others (magnetic GO NCs), which would be significantly more costly to separate from solution through the requirements of magnetic field. Therefore, the novel GO/Mg(hydr)oxide NCs are promising adsorbents and can be further tested for the successful removal of other pollutants from water and wastewater. The results showed that although the adsorption capacity of MB onto the NC was significantly high with 833 mg/g, the adsorption capacity of BPA was not as high as expected (119 mg/g). This could be due to the anionic structure of the BPA, compared to the cationic MB dye. The specific characteristics that control the adsorption of organic solutes onto the NC with particular emphasis being the strength of chemical bonds between the compound and the adsorbent is proposed to be investigated in Phase II. Several EDCs and other organic contaminants will be selected based on solute charge and hydrophobicity to be tested for this purpose. The high adsorption capacity of MB onto the NC (833 mg/g) will be used as a benchmark for the selected EDCs. The positive findings obtained especially for MB sorption warrant further investigation of the efficient removal of EDCs in solution using the synthesized NC. Our results indicate a high potential for the proposed technology to be transferred and adapted at any water treatment plant unit with a long term viability.
Supplemental Keywords:
Graphene oxide, magnesium oxide, bispehol A, methylene blue, adsorption, nanoparticlesThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.