Using raw bamboo waste to sustainably remove toxic dyes from water

Summary

Water is a fundamental human right, yet over 780 million people worldwide do not have access to clean water. A majority of this problem stems from human-caused dye pollution: we regularly use anionic dyes in the paper, petroleum, and textile industries. The effluents contribute significantly to global water pollution that harms important microbial populations and can be toxic to mammals. While there are some attempts to solve the issue at hand, current techniques of dye removal are inefficient and expensive, making them infeasible for large-scale use in developing and third-world countries, where accessibility of water is the largest concern.    

My main goal was to devise a cheap and sustainable method to remove these harmful dyes. Research informed me that China and India are the biggest producers of bamboo waste, yet no one is using this waste for any purpose—it is just waste. I wanted to make this waste reusable, so I extracted the cellulose from it and used an oxidation and cationic reagent to modify the functional groups of the cellulose so that they would become positively charged, and would thus electrostatically attract the negatively charged dyes. This method is known as adsorption, and it’ll change millions of lives as it's the fastest and most affordable way to remove dyes since it’s the first method ever to rely 100% on raw bamboo waste as the biomass source. Results showed adsorption capacities of this method to greatly exceed published data, paving the way for applications in both industrial and on-the-site settings.

Question / Proposal

Chemical methods of dye removal from water, such as electrolysis, are the most common but are very expensive and thus not accessible. Additionally, most of these methods produce chemical byproducts, simply shifting the problem elsewhere. Physical methods of removal, such as adsorption, are thus preferred. Cellulose is the most abundant polymer, but it has many problems such as high crystallinity, hindering its reactivity.

Primary question: Is it possible to create a more effective and affordable method of water purification that is based entirely on using cellulose from biomass waste that can be modeled by developing and third-world countries where the lack of access to clean water is most severe?

Hypothesis: A new and efficient method of water purification can be developed by modifying the chemical properties of cellulose extracted from raw bamboo waste, producing a cheap and biodegradable adsorbent that doesn’t rely on advanced technologies and produces zero waste or byproducts.

I focused on devising a method of using cellulose from bamboo waste for dye adsorption. To modify the chemical properties of cellulose, I figured out an oxidation and cationic reagent could be used to synthesize a cellulose derivative called cationized dialdehyde cellulose (cDAC). cDAC is a much better alternative compared to just cellulose as it’s reactive, can be synthesized in water solution, it’s biodegradable, and most importantly, the cationic reagent formed positively charged functional groups, which multiplies the attraction of the negatively charged dye molecules to the adsorbent, allowing for easy removal of the dye and producing clean water.

Research

Dye Removal Applications and Techniques

Commercial dyes are commonly used in the textile, paper, dyeing, and petroleum industries, and the chemicals are frequently released into water sources, contaminating the water that millions of people are dependent upon.

Dyes cannot be removed using conventional wastewater treatment methods since dyes cannot be biodegraded. Some techniques to remove dyes have been developed, but they are largely inefficient and expensive, making them inaccessible. Figure 1 outlines the common dye removal techniques. Chemical methods of removal are most relied upon, but these produce harmful byproducts. Cellulose also has been long investigated, as it is the most abundant natural polymer, but its highly ordered hydrogen bond network and high crystallinity make it not very reactive or efficient.

Using Biomass

In order to create a method of water purification that has the capability to provide water to people, all the problems outlined above need to be resolved. To do this, this project focuses on using the cellulose from biomass, specifically bamboo waste. Bamboo waste is extremely useful, as there are thousands of tons just sitting around as waste, it avoids producing byproducts, and chemical modification can enhance its reactivity.

—Information from other research allowed me to form 4 main objectives for my project:—

—1. Prepare dialdehyde cellulose (DAC) from bamboo pulp

—2. Optimize the cationization process for the preparation of cationized DAC (cDAC)

—3. Explore the efficiency of cDAC in adsorbing congo red

4. Characterize the cDAC to further understand its adsorption abilities

Congo red was chosen as the dye to be tested in these experiments because it is the most common anionic dye that is found in wastewater, and it can be modeled to all anionic dyes. Figures 2 and 3 show the structure of the dye, and what it looks like at 100 mg/L concentration.

Adsorption

While no other studies have used bamboo waste specifically to adsorb dyes, general ideas were built upon to allow this project to come to fruition. The literature review was particularly useful in developing the protocols for the time and pH studies, as well as for the scanning electron microscopy. Additionally, I was able to gain a lot of insight on the isotherm and kinetic models, as well as learn how to apply them to my own data. I was also able to read a variety of papers about the potential uses of sodium periodate as an oxidizer, and girard’s reagent T’s ability to be a cationic reagent, which helped form the major reaction to produce cDAC.

The most important thing about cDAC is that is adsorbs dyes based on electrostatic charges, enabling it to adsorb much more dye than other methods as well as happen much faster since there is a driving force. This makes cDAC a great adsorbent to apply to wastewater treatment facilities as well as on-site locations that are severely impacted by dye contamination. This can specifically be done by exploring the use of cross-linkers to form cDAC membranes and foams.

Method / Testing and Redesign

The following experiments were conducted:

1. Preparation of dialdehyde cellulose (DAC)

Bamboo pulp was made by blending bamboo waste with water until a well-mixed pulp formed. The pulp had a 1.5% weight percentage of cellulose.

To oxidize the hydroxyl functional groups on cellulose into aldehyde groups, 4 mmol of NaIO4 (sodium periodate) per 1 gram of cellulose was added to the bamboo pulp, mixed at 55°C for 24 hours, producing DAC (Figure 4).

 

The DAC was placed into molecularporous membrane dialysis bags to wash away the excess sodium periodate (Figure 5).

 

2. Preparation of cationized dialdehyde cellulose (cDAC)

To convert the aldehyde groups on DAC into positively charged functional groups, girard’s reagent T ((2-hydrazinyl2-oxoethyl)-trimethylazanium chloride) was added to form imine bonds and quaternary ammonium groups (Figure 6). To explore the efficiency of the cationization process, the molar ratio of girard’s reagent T was manipulated. Four conditions were used: 1x molar ratio at room temperature (RT), 2x molar ratio RT, 3x molar ratio RT, and 3x molar ratio at 40°C. The 3x molar ratio was tested at different temperatures because of preliminary confirmation that it works at room temperature. All reactions lasted 72 hours.

The cDAC was placed into molecularporous membrane dialysis bags again to wash away the excess chemicals to prevent interference with characterization.

3. Adsorption tests on congo red

Adsorption tests were conducted in sterile 25 mL vials (Figure 7). The concentrations of congo red tested were 10, 25, 50, 100, 200, 400, 600, 800, 1000, and 1500 mg/L. Vials were prepared in triplicates for each concentration. Each vial was filled with the calculated amount of dye solution and cDAC suspension (used concentration of suspension to measure 10 mg of cDAC).

The vials were placed in a shaking bed for 24 hours after the cDAC was added. In order to test the purity of the water post-adsorption, the cDAC was removed from the solution by spinning the solution in a centrifuge at 10,000 rpm for 20 minutes. The solution was then taken for ultraviolet–visible spectroscopy, as the absorbance readings were needed to calculate the maximum adsorption capacity.

4. Further Modeling and Characterization

The data was applied to two isotherm models (langmuir and freundlich) and four kinetic models (pseudo-first-order, pseudo-second-order, elovich, and step I and step II of intraparticle diffusion) to learn more about the mechanism of adsorption. A time and pH study were also conducted to explore the properties and efficiencies of adsorption.

Lastly, the morphology, structure, and cationic degrees were investigated through the following tests:

Morphology: Scanning Electron Microscopy

Structure: Fourier-Transform Infrared Spectroscopy

Cationic Degree: Zeta Potential

Safety Protocols

All of the experiments were conducted in the Hsiao Lab in the Department of Chemistry at Stony Brook University. Extensive safety precautions were taken in accordance with protocols established by Stony Brook University and the Environmental Health and Safety. This includes wearing personal protective equipment such as a lab coat and safety goggles, completing extensive safety training, and adhering to proper waste disposal regulations.

Results

Adsorption Mechanism - Properties and Modeling

The absorbance readings from UV-Vis were used to calculate Q (the mg of dye adsorbed per g) using

Equation 1: ((C0-Ce)*V)/M

where Ce and Co are the equilibrium and inital dye concentrations (mg/L), and M is adosrbent mass (mg).

Figures 8 and 9 respectively show the data conformed to the langmuir and freundlich isotherm models to study the adsorption mechanism. R2 values are used to confirm whether or not the model applies to the data (values need to be close to 1.0000). The R2 values (Table 1) confirm that the adsorption mechanism of cDAC fits the langmuir isotherm model. The langmuir model is expressed in the following linear form:

Equation 2: Ce/qe = 1/(qmKL) + Ce/qm

where qm is the maximum dye adsorption (mg g-1), and KL is the adsorption equilibrium constant (L g-1).

The Qm (maximum adsorption capacity) values allowed for comparison of the four cDAC conditions. The Qm was found by calculating 1 divided by the slope of each line from the langmuir model. Table 2 shows Qm values of adsorbents currently published. The Qm values for the cDAC are shown next to Table 2, ranging from 666 to 909 mg/g, significantly larger than the adsorption capacities of other adsorbents. Additionally, removal efficiencies reached over 99% for the average concentration of congo red in wastewater (Figure 10).

The 3x room temperature and the 3x 40°C are the most effective materials for adsorption and thus further experiments were only conducted on these two.

The pseudo-first-order and the pseudo-second-order kinetic models were also used to analyze the adsorption mechanism. The experimental data were fitted linearly, as shown in Figures 11 and 12. The kinetic parameters summarized in Table 3 show the R2 values are closer to 1.0000 for the pseudo-second-order than pseudo-first-order kinetic model. The data did not fit well to the elovich or intraparticle diffusion models (low R2 values). The linear form for pseudo-second-order is expressed as:

Equation 3: t/qt = (1/k2qe2) + (t/qe)

where qe (mg g-1) is the adsorption capacity in equilibrium.

cDAC Properties and Characterization

The adsorbent itself was characterized to explain its significant ability to adsorb dye. Figure 13 shows the scanning electron microscopy pictures. The 3x room temperature and 3x 40°C fibers seem to have more porous and fluffy-like textures. Figure 14 provides information about the structure, as the peaks correlate to functional groups. The presence of aldehyde groups on the DAC and the presence of imine bonds on the cDAC are confirmed.

The time study showed that adsorption is completed in under 15 minutes for the 3x room temperature and within 60 minutes for the 3x 40°C (Figure 15). Zeta potential is a measurement of the charge of the cDAC. Figure 16 shows a correlation between pH and degree of cationicity, leading to a pH study (Figure 17) that showed that adsorption ability is increased significantly by adjusting the pH of the cDAC suspension to be acidic, and hindered if the pH of the suspension is basic. 

 

Conclusion

Conclusions

My experimental results support my hypothesis, as the cDAC adsorbent is a new and more effective method of water purification. The Qm values for cDAC are largely unmatched by any published adsorbents, and no advanced engineering technologies were needed.

The results concluded that the adsorption of congo red fits the langmuir isotherm model, which means that congo red is being adsorbed through monolayer adsorption as opposed to multilayer adsorption (freundlich). It also informs us that the active surfaces of cDAC are finite and are exactly identical. The adsorption mechanism was also found to obey the pseudo-second-order kinetic model. This suggests that the adsorption of congo red is controlled by the chemisorption behavior (as opposed to physical adsorption for pseudo-first-order), attributed to exchange or sharing of electrons between anion groups of dye and cation groups of the cDAC.

The 3x room temperature and 3x 40°C exemplified more porous and fluffy-like textures, providing a possible explanation for their adsorption abilities, as fiber size and texture can determine dye interaction. The FT-IR served as a confirmation of the reactions and the zeta potential graph corresponded with the pH study to show that the adsorption capacity can actually be improved greatly by altering the pH of the wastewater before adsorption. Figure 18 depicts a mechanism to explain this: in acidic conditions, certain functional groups gain a proton (making them charged) allowing for more electrostatic attraction and thus adsorption.

Sustainability

Using cDAC as a water purification technology is extremely safe and eco-friendly, as no byproducts are produced and it’s 100% biodegradable since it’s made from bamboo waste. Materials used to produce cDAC are inexpensive, making this method accessible. The time study also showed that the adsorption process can finish in less than 15 minutes, making this process extremely efficient and sustainable, as other methods of water purification can take 24-48 hours.

Future Experiments

There are two major experiments I would like to focus on to create numerous applications of cDAC:

1) Adding cross-linkers to cDAC to create a filter that has electrostatic adsorption properties.

2) Creating an environment-friendly cDAC foam that can directly be applied to wastewater. This can be designed to incorporate other purification technologies to remove all sorts of harmful things such as bacteria, viruses, and heavy metals with just one foam. 

cDAC can be applied to a porous material, allowing for applications in a wastewater facility (Figure 19). A cDAC membrane (described above) can also be used to ensure all the dye is removed.

Societal Impact

The impact of this research is significant, as this method can improve the lives of millions of people that are suffering from not having access to clean water. This is especially true since over 99% of the dye is able to be removed at its average concentration found in wastewater. Furthermore, utilizing waste that is being produced in the status quo, like bamboo waste, is key for us to develop a sustainable future while helping both developing and developed countries during crises.

About me

My name is Akash Rathod. I am a senior in high school and live in Michigan. The global water crisis is very personal to me, as it has impacted my friends, family, and community. I have watched the crisis of lead contamination in Flint, Michigan unfold right in front of me. Additionally, I have family in India and have seen lines of people outside of a hospital waiting for treatment from water-borne illnesses. Doctors can only do so much to ameliorate symptoms, making it clear that the best medicine is prevention, which can only be achieved by water purification techniques. I thus went to Stony Brook University in New York this past summer, where I devised the first adsorption method using raw bamboo waste in the Hsiao Lab.

Winning the Google Science Fair will help me transform my research from theory to praxis. I do not want my method to become just another research publication—I want it to leave the laboratory and create a lasting impact in the world. Additionally, the prize will provide the opportunity to share my ideas with the world, to not only changes lives materially, but to also inspire students to recognize the change they can create. I am hoping to attend Harvard University to pursue my passion for scientific research and to make progress in solving the water crisis.

“To me there has never been a higher source of earthly honor or distinction than that connected with advances in science.”

-Isaac Newton

Health & Safety

Contact Information

All the experiments were conducted in the Hsiao Lab in the Department of Chemistry at Stony Brook University. Professor Benjamin Hsiao is the PI of the lab, and Xiangu Huang is the graduate student that I worked with closely. Their contact information is listed below:

Email: Benjamin.Hsiao@stonybrook.edu

Phone: (631) 632-7793

Email: xiangyu.huang@stonybrook.edu

Phone: (631) 682-1370

The Laboratory's Address: Room 479 - John S. Toll Drive, Stony Brook, NY 11794

Health and Safety

This project had very minimal risks as the only major concerns were being cautious with the equipment, and making sure I was protected thoroughly and prepared to work the congo red dye, given that it is toxic. I was under adult supervision at all times while I was working in the lab, even if the adult was not directly working with me as all the physical research was completed by me. Before I could work in the lab, I had to undergo extensive safety training, including online examinations and on-site training. I wore personal protective equipment at all times includings gloves, a lab coat, and safety goggles.

The Hsiao Lab is part of the Laboratory Safety program. As stated on their website, this "supports Environmental Health and Safety’s Mission by providing guidance and support to researchers in order to identify and eliminate or reduce hazards, train personnel, and ensure compliance with local, state and federal regulations. The Laboratory Safety program provides policies, procedures, training, guidance, and other information to assist research and teaching personnel to provide a safe and healthful environment in which to operate."

Attached are the policies and procedures that were followed throughout experimentation (links provided as well due to formatting issues from pdf to google docs):

1. The Laboratory Safety Policy establishes the requirements for protection from potential exposures to hazardous materials and processes found in labs at Stony Brook University. (https://ehs.stonybrook.edu/commcms/environmental-health-and-safety/programs/laboratory-safety/_docs/Laboratory%20Safety.pdf)

2. The Chemical Hygiene Plan provides information and requirements for working with hazardous materials. (https://ehs.stonybrook.edu/commcms/environmental-health-and-safety/programs/laboratory-safety/Chemical%20Hygiene%20Plan.pdf)

3. The Chemical Storage Guide outlines storage requirements for all chemicals and how to avoid incompatibility. (https://ehs.stonybrook.edu/commcms/environmental-health-and-safety/programs/laboratory-safety/chemical-safety/Chemical%20Storage%20Guide.pdf)

4. The Chemical Spills outlines the procedures in place in the event of a chemical spillage. This was important when working with the sodium periodate, girard’s reagent T, and congo red as we had to be prepared in the event of spillage. (https://ehs.stonybrook.edu/programs/laboratory-safety/laboratory-emergencies/chemical-spills.php)

5. The PPE Selection Guide assisted in selecting the most appropriate personal protective equipment, with an emphasis on glove selection. (https://ehs.stonybrook.edu/commcms/environmental-health-and-safety/programs/laboratory-safety/personal-protective-equipment/PPE%20Selection%20Guide.pdf)

6. The Lab Training Checklist goes over the specific lab training requirements I had to complete before I could do research in the laboratory. (https://ehs.stonybrook.edu/commcms/environmental-health-and-safety/programs/laboratory-safety/general-laboratory-safety/New%20lab%20worker%20training%20checklist.pdf)

Bibliography, references, and acknowledgements

Acknowledgements

This past summer at Stony Brook University has truly changed my perspective of the world—I not only learned that I can make a change in the real world through research, but I was pushed to new levels of personal growth, as directing my time and energy towards research in a lab setting requires extreme responsibility and diligence, especially since I got to manage my own projects.

I am extremely grateful to Xiangyu Huang and Professor Benjamin Hsiao for mentoring me and providing me with the necessary facilities to allow my project to come to fruition. They not only taught me about the field of water purification, but they helped me gain independence in the laboratory by constantly helping my refine my experimental protocols as well as helping me create a coherent explanation of my results. Through their guidance, I was able to complete all the experiments listed in my methods section (preparation of bamboo pulp, preparation of DAC, preparation of cDAC, adsorption, and all the characterization) on my own in the laboratory while under their supervision. I was also able to have access to special equipment to allow me to conduct precise characterization, such as the UV-Vis spectrometer, a zeta potential reader, centrifuges, a scanning electron microscope, and a FT-IR spectrometer.

I am also thankful for my wonderful STEM teachers at Okemos High School, especially Mrs. Karen Canestraight and Mrs. Colleen Palmer for helping me learn all the essentials of chemistry and biology and making me realize that this is what I wanted to pursue and apply through scientific research. Lastly, I would also like to thank my parents for constantly supporting me in my research and science endeavors, allowing me to pursue something that is very meaningful to me.

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