National Science Foundation     |     Directorate for Engineering  (ENG)
Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)
CBET Research Highlights 
Notable Accomplishments from CBET Awards
1417 - Part A - Novel Adsorbents for Heavy Metal Removal from Polluted Water
Zhanhu Guo  -  Lamar University Beaumont

Outcome or Accomplishment:  Researchers at Lamar University have demonstrated the extraordinary ability to remove chromium from polluted waters using nano-sized sponge-like adsorbents.  The researchers have also demonstrated that the adsorbents and the adsorbed pollutant can be quickly recycled by simply applying a magnet.

Zhanhu Guo Image 1
    Figure 1.  Transmission electron microscopy (TEM) images of the magnetic graphene nanocomposites (MGNCs) with a nanoparticle loading of 10 weight percent (wt%).  (a) The nanoparticles are uniformly distributed on the graphene sheet, and (b) high-resolution TEM image showing the core@shell structure of the nanoparticles independent of the particle size, top inset shows the core@double-shell structure of one individual nanoparticle.
Zhanhu Guo Image 2
    Figure 2.  Energy filtered Transmission electron microscopy (TEM) of the Magnetic Graphene Nanocomposites (MGNCs)
(a) zero-loss image,
(b) Iron (Fe) map,
(c) Oxygen (O) map,
(d) Sulfur (S) map,
(e) Silicon (Si) map,
(f) Carbon (C) map,
(g) Fe+O map,
(h) Fe+S map and
(i) Fe+O+S+Si map.
Zhanhu Guo Image Image 3
    Figure 3.  (a) High-resolution transmission electron microscopy (HRTEM) of a single particle showing an iron core surrounded by a double shell structure, where the top-left inset gives a closer view on the lattice fringes of inner shell showing an interlayer distance of 2.52 angstroms () corresponding to the (311) plane of iron oxide, and the bottom right inset gives a closer view on the lattice fringes of the core showing an interlayer distance of 2.03 corresponding to (110) plane of iron.  (b) shows the MGNCs dispersed in acid and (c) the magnetic separation using a permanent magnet.  The magnetic graphene nanocomposites (MGNCs) are tested to be stable over 4-hour immersion in 1 molar (M) of hydrochloric acid (HCl) solution.
Credit for All Images:  Zhanhu Guo, Lamar University, Beaumont, TX

Impact:  This novel material is highly efficient with an adsorption time of a few minutes, significantly faster than conventional adsorbents that take up to hours and even days.  This new process also satisfies the Environmental Protection Agency (EPA) requirement for the treatment of wastewater containing low concentrations of chromium pollutants.

Explanation/background:  In NSF-supported research, Professor Guo and his team at Lamar University in Beaumont, Texas have demonstrated the success of Magnetic Graphene Nanocomposites (MGNCs) for fast chromium removal from polluted water.  Currently, activated carbon is used to remove the pollutants.  Graphene is a special form of carbon whereby the carbon atoms are arranged in a one atom thick layer.  This makes graphene an excellent material for adding magnetic nanoparticles on the surface.

CBET Research Highlight - Part B - Engineering Technical Information

1417 - Novel Adsorbents for Heavy Metal Removal from Polluted Water

Zhanhu Guo  -  Lamar University Beaumont

Background:  Effective adsorbents for the removal of heavy metal ions (chromium VI, Arsenic III and Arsenic V) from polluted water are in urgent need to satisfy the new EPA requirement.  Carbon based nanostructures are the most promising material for the next generation of highly efficient adsorbents.  Graphene has been widely studied for energy storage and electronic device applications.  However, to deploy graphene in the environmental field has been limited investigated and related knowledge is required.  The high specific surface area of graphene makes it an excellent substrate for decorating nanoparticles on its surface and allows its corresponding nanocomposites to be applied for various applications.  Magnetic graphene nanocomposites (MGNCs) with a controlled intrinsic structure have enormous promise as novel adsorbents for purifying wastewater containing low concentrated heavy metals, which challenges the current existing technologies including the adsorption by sole activated carbon.
In NSF-supported research, Professor Guo and his team at Lamar University in Texas have successfully demonstrated a facile method to fabricate MGNCs and proved its success in fast chromium (VI) removal from polluted water.  These novel magnetic nanocomposite adsorbents make the recycling process much easier.  By simply applying a magnet, the researchers have demonstrated that the adsorbents and the adsorbed heavy metals can be quickly recycled.  The heavy metal can be released from adsorbents by adjusting pH of the solution.

- 1 -  By carefully choosing the iron precursor, the team has developed a facile thermodecomposition method to synthesize MGNCs.  The particles are uniformly dispersed on the graphene sheet with a narrow size distribution.  High-resolution transmission electron microscopy and energy filtered elemental mapping revealed a core@double-shell structure of the nanoparticles with crystalline iron as the core, iron oxide as the inner shell and amorphous Si-S-O compound as the outer shell, Figures 1 and 2.
- 2 -  The team investigates the adsorption kinetics of this novel adsorbent and finds out that the adsorption kinetics follows the pseudo-second-order model with a high adsorption capacity of 1.03 mg/g and larger adsorption rate coefficient of 0.28 g/mg/min.  At different pH conditions, a complete Cr(VI) removal was achieved in acidic solutions when the pH is between 1 to 3 rather than in neutral and basic conditions.
- 3 -  The large saturation magnetization (96.3 emu/g) of the synthesized nanoparticles allows fast separation of the MGNCs from liquid suspension, Figure 3.  By using a permanent magnet, the recycling process of both the MGNCs adsorbents and the adsorbed Cr(VI) is more energetically and economically sustainable.

Summary:  A facile one-pot synthesis method to obtain MGNCs decorated with core@double-shell NPs is presented.  The mono-dispersed NPs on the graphene sheet, composed of a crystalline iron core, inner iron oxide shell, and the outmost amorphous Si-S-O compound shell, are highly stable even immersed in 1 M HCl aqueous acid.  The MGNCs show an extremely fast Cr(VI) removal performance to reach a complete removal with only 5 min.  However, other materials, like carbon, waste biomass and lignocellulosic substrate, often require hours even days of treatment and still the Cr(VI) could not be removed completely.  The pseudo-second-order kinetic model best describes the adsorption behavior of the Cr(VI) on MGNCs.  These materials show their highest adsorption capacity at relatively lower pH value solutions.  These novel MGNCs exhibit a bright future for their applications in heavy metal removal from the wastewater.

Scientific Uniqueness:  This NSF-funded research project is unique because it has generate a novel adsorbent that is capable of fast and complete removal of heavy metal ions from polluted water.  The extensive and unique breadth of the project has provided a general method to fabricate multi-functional magnetic graphene hybrids with a facile one-pot approach.  And the produced magnetic adsorbents can be used to treat polluted water that contains various heavy metal ions.  In addition, novel energy-free recycling process using a permanent magnet would be used for this new generation of adsorbent.

Strategic Outcome Goals:
- 1Discovery:  The NSF-funded research is aimed at manipulating intrinsic structures of magnetic carbon nanocomposites (MCNCs) with different organic-inorganic hybrids and to evaluate their heavy metal removal performance.  These materials can be applied in a magnetic field assisted process to tackle the central environmental remediation technique challenge.  This process would be amenable to easy-recycling MCNCs and heavy metals.  In addition, the development of novel adsorbents has allowed the research team to discover the intrinsic structures of MCNCs and reveal the structure-property relationship regarding the heavy metal ions removal performance.
- 2Learning:  This project has provided training and research experience to two full-time PhD candidate graduate students.  The approved REU grant will support about two undergraduate students in the Chemical Engineering department at Lamar University.

Transformative Research:  This funded research is potentially transformative because the novel adsorbents show great advantages compared to other adsorbents, such as the high adsorption capacity, fast removal efficiency, and stability in acid environment.  Most importantly, these magnetic adsorbents can be easily recycled using a permanent magnet, which is an environmentally and economically energy-free processing.  The future practical application of these materials will definitely enhance the quality of drinking water and also help to improve the quality of people's daily life.

Intellectual Merit:  The objective of this research is to manipulate intrinsic structures of MCNCs with different organic-inorganic hybrids and to evaluate their heavy metal removal performance.  A magnetic field assisted process with the aid of novel MCNCs to tackle the central environmental remediation technique challenge is applied.  This process would be amenable to easy-recycling MCNCs and heavy metals.  The challenge of the proposed project is to determine the optimum MCNCs for heavy metal removal.  The research efforts are grouped into three closely coupled research thrusts: (1) synthesis of different organic-inorganic hybrids from both commercial and lab-made nanoparticles: both thin films and nanofibers will be prepared, with various physicochemical structures, (2) preparation of a new family of MCNCs with controllable nanostructure (solid, porous and semi-permeable) by the obtained optimum fabrication process (stabilization and carbonization temperature and time), and (3) heavy metal removal performance test.  This will advance the knowledge required to provide next-generation multifunctional adsorbents and provide transformative environmental remediation nanotechnology.

The Broader Impacts of this research include:
- 1Benefits to society:  This work makes a significant impact on the rapidly developing field of adsorbents.  The field assisted separation process with the aid of MCNCs makes the treatment of the wastewater containing lowly concentrated heavy metals satisfying the stringent EPA requirement for the released Cr(VI).  The intimate connection with the companies will foster quick commercialization of the new environmental nanotechnology and expedite the techniques in serving society/community.
- 2Broadening participation of underrepresented groups:  Approximately 50% of the population in Lamar Community is African American.  The project has involved one female student and one African American.  Both are from Chemical Engineering.
- 3Advancing discovery and understanding while promoting teaching, training, and learning:  The fundamental studies provide a basis to explore novel MCNCs in an engineering way integrating the chemistry, chemical/environmental engineering, materials science and engineering, and electrochemistry into one research topic.  This interdisciplinary project will definitely create many noteworthy opportunities for education and training.  K-12 outreach, undergraduate education, international impact and curriculum development are detailed.  Strong bondage with industry will bring job opportunity.  Underrepresented and female students are highly emphasized in this project.
- 4Enhancing the infrastructure for research and education:  The researchers have built connections with several companies, which will facilitate the practical commercialization of the products.
- 5Results disseminated broadly to enhance scientific and technological understanding:  The findings from this research are being disseminated broadly in international scientific journals as well as through presentations made at international conferences and invited talks.  Especially, the poster presentations at AIChE conference 2011 have been selected the First and Second place awards in the Environmental Division, and Third place award in the Materials Engineering and Sciences Division.

Program Director:
Rosemarie Wesson
CBET Program Director - Chemical and Biological Separations
NSF Award Number:   1137441
Award Title:   EAGER: Magnetic Carbon Nanocomposites for Heavy Metal Removal from Polluted Water
Principal Investigator:   Zhanhu Guo
Institution Name:   Lamar University Beaumont
Program Element Code:   1417
CBET Research Highlight:   Fiscal Year 2012
Approved by CBET on:   23 March 2012

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This CBET Research Highlight was Updated on 10 April 2012.