I specialize in the hydrothermal liquefaction of lignin and aquatic biomass, with a particular focus on producing functional chemicals. I explored diverse thermochemical techniques, including hydrothermal liquefaction and pyrolysis, for efficient biomass conversion. In addition, my work involved the synthesis of non-noble metal catalysts and activated carbon catalysts derived from biomass, demonstrating remarkable activity and selectivity in various reaction conditions. As a postdoctoral fellow at Auburn University, my current research extends this expertise. I am actively involved in developing sustainable processes for fuel and chemical production from biomass using innovative heterogeneous metal catalysts. My work also includes the production of modified biochar from biomass for effective wastewater treatment. In addition to conducting cutting-edge research, I am passionate about mentoring students, facilitating their hands-on experience, and guiding them in preparing research proposals for funding opportunities. My research interests encompass a wide array of analytical techniques, including Total Organic Carbon analysis, FT-IR, CHNS analysis, TGA, BET analysis, GC-MS, and ICP-OES, among others. This proficiency, along with my ability to guide students in experimental work and research project proposal writing, demonstrates my commitment to advancing scientific knowledge.
Lignin conversion into high value chemicals:
The valorization of lignin, an abundant bio-aromatic resource, is crucial for sustainable bioproducts. Non-catalytic hydrothermal liquefaction of alkali lignin typically yields minimal bio-oil with low selectivity. However, catalytic approaches significantly enhance both yield and the selectivity of valuable compounds. Earlier research demonstrated that using a Ni-Co/AC catalyst at 280 °C with ethanol solvent achieved a high bio-oil yield of 72.0 wt%, with Co/AC and Ni-Co/C selectively producing vanillin (34–36.2%). To further improve compound selectivity, researchers have developed low-temperature liquefaction processes (140-160 °C) using acid/base catalysts. For instance, while a base catalyst yielded 26 wt% bio-oil, formic acid increased it to 78 wt% with 36% lignin selectivity. Further advancements involved synthesizing efficient solid base catalysts like CaO/CeO2 and CaO/ZrO2, which yielded 50.0 wt% bio-oil at 180 °C using methanol/ethanol. Notably, CaO/CeO2 in methanol achieved the highest vanillin content (62.2%). More recent studies exploring lignin oxidation for bio-oil and phenolic compounds have also shown promising results with metal catalysts. For example, zirconium oxide (ZrO2)-supported bimetallic Ni-Co catalysts boosted bio-oil yield to 67.4 wt% from 35.3 wt% in non-catalytic oxidation, significantly increasing vanillin yield (43.7%) by selectively cleaving the ether β-O-4 bond in lignin. Similarly, cobalt (Co) supported on calcium oxide (CaO) catalysts for lignin depolymerization achieved a 60.2 wt% bio-oil yield with methanol, enhancing vanillin selectivity to 58.7% and improving the bio-oil's heating value to 35.5 MJ/kg. This Co/CaO catalyst also exhibited excellent recyclability.
Current Challenges and Future Directions:
While catalytic approaches consistently demonstrate maximum bio-oil yield and higher selectivity towards valuable compounds, the efficient separation of these compounds from the complex bio-oil mixture remains a significant challenge. Future work is focusing on improving this separation process to enable the rational design and development of scalable, green, and sustainable technologies for vanillin synthesis from biorefinery lignin. Alternatively, the obtained bio-oil can undergo hydrogenation to produce cycloalkane-rich bio-oil, suitable for sustainable aviation fuel (SAF) production using novel catalysts and optimize process parameters.
Aquatic Biomass and food waste Liquefaction:
Biomass, encompassing agricultural, forest, municipal solid waste, animal waste, food processing waste, and aquatic residues, offers a promising renewable alternative to fossil fuels for both energy and chemical production. Various technologies, including biological, physical, and thermochemical conversion, are employed for biomass utilization. Among thermochemical processes like pyrolysis, hydrothermal liquefaction (HTL), and gasification, HTL is particularly well-suited for wet biomass (such as aquatic biomass and wet food waste) as it bypasses the need for costly drying, making it industrially viable.
HTL of Aquatic Biomass:
Recent studies highlight the efficacy of HTL for aquatic biomass. For instance, HTL of Sargassum tenerrimum at 280 °C with ethanol yielded 23.8 wt% bio-oil, notably rich in aliphatic esters (46–52%). Similarly, Azolla filiculoides produced 24.3–28.8% bio-oil with methanol and ethanol, significantly more than with water (13.6–21.5%), with hexadecanoic acid methyl (45.0%) and ethyl esters (54.4%) being predominant. The use of a CaO/ZrO₂ catalyst in a water-ethanol co-solvent system further improved bio-oil yield to 33.0 wt% with 89% esters. Catalytic liquefaction also enhanced bio-oil quality by reducing nitrogen and oxygen content.
HTL of Wet Food Waste:
Catalytic HTL is also a promising strategy for converting wet food waste (FW) into high-quality biocrude, mitigating emissions and recovering valuable resources. Research on catalytic HTL of FW using cobalt (Co), magnesium (Mg), and bimetallic cobalt-magnesium (Co–Mg) supported on ZSM-5 demonstrated significant improvements. A maximum biocrude yield of 60.89 wt% was achieved with the bimetallic Co–Mg/ZSM-5 catalyst at 280 °C (10 wt% catalyst, 15 min reaction time). This catalytic process, especially with ethanol as a solvent, resulted in a higher percentage of ester compounds (74.15%) and improved biocrude quality, characterized by lower oxygen and nitrogen content and a higher heating value (HHV). The biocrude also contained 12.16 wt% linoleic ester compounds. Moreover, the optimal Co–Mg/ZSM-5 catalyst exhibited excellent reusability and stability in FW liquefaction. These advancements underscore the potential of optimized HTL processes and novel catalysts in efficiently converting diverse biomass feedstocks into valuable biofuels and biochemicals.
Current Challenges and Future Directions:
This study developed an efficient hydrothermal liquefaction (HTL) process to produce fatty acid esters from algae and food waste (FW), yielding high-quality biocrude. These valuable esters are versatile, serving as diesel fuel, lubricant base oil, or fuel additives. This innovation has significant industrial potential and promotes sustainable waste reuse. Future research will focus on separating and purifying these fatty acid esters using methods like solvent extraction and distillation. Additionally, the biocrude will be upgraded via deoxygenation and hydrogenation catalysts to produce high-quality biofuels for transportation.
Phosphorous and Nitrate adsorption
To protect ecosystems, efficient wastewater treatment for nutrient removal is crucial. This research explored using biochar-derived adsorbents for phosphorus (P) and ammonium nitrogen (N) removal. One study we developed zinc chloride-activated biochar (BC–Zn) adsorbent, which is reached 100% P adsorption at 10 mg/L, with capacity increasing from 0.13 to 10.4 mg/g as P concentration rose from 5 to 200 mg/L. P adsorption followed Langmuir and quasi-second-order kinetics, primarily via precipitation. Another study we synthesized magnesium (Mg), iron (Fe), and Mg/Fe doped biochars. Mg/BC adsorbent and adsorbent demonstrated superior performance, adsorbing P and N individually (64.65 mg/g P; 62.50 mg/g N) and from mixtures (30.3 mg/g P; 27.67 mg/g N). It also effectively removed P (88.30%) and N (59.36%) from real wastewater. Adsorption kinetics followed the pseudo-second-order model, with Langmuir isotherms for N and Freundlich for P. Thermodynamic studies confirmed spontaneous and feasible adsorption. These findings highlight that strategic biochar modification is key to developing effective nutrient removal technologies for wastewater treatment.
Current Challenges and Future Directions:
Adsorbent Mg/BC is very effective for adsorbing P and N from the aqueous system which could prevent the eutrophication of natural water. However, in the case of actual wastewater, the efficiency was lower, likely due to the wastewater containing other impurities such as metals, inorganics ions, and organic materials which inhibited the P and N adsorption. Further research is needed to identify a suitable adsorbent to reach 100% adsorption potential. Further, a continuous adsorption system needs to be developed to utilize the adsorption capacity effectively. In addition, after the adsorption of the P and N in the wastewater, the adsorbent could be applied as a fertilizer source in agriculture, potentially reducing synthetic fertilizer use.
In summary, my research interests revolve around harnessing thermochemical processes, catalyst development, and sustainable biomass utilization to address pressing environmental and energy challenges.
Research Interests: Biomass conversion, Pyrolysis, Hydrothermal Liquefaction, Lignin valorization, Catalysis, Biochar, Adsorption, Bio-oil Upgrading,