Catalysts for Circularity: Fuels, Polymers & Clean Water

Electrochemical coupling of biobased platform molecules can lead to highly branched isoalkanes and cyclic hydrocarbons which are otherwise difficult to access from biomass feedstocks. Mesityl oxide and isophorone are produced by the base-induced self-condensation of biogenic acetone and can be electrochemically coupled in a simple undivided cell to give oxygenates that are catalytically hydrogenated to branched C₉, C₁₂, C₁₅, and C₁₈ hydrocarbons. The resulting product was shown to exceed the specifications for commercial Jet A fuel. Likewise, lignocellulose-derived levulinic acid couples at the anode with the loss of carbon dioxide to give a C₈ dione that undergoes intramolecular aldol condensation, yielding a branched cycloalkane after hydrodeoxygenation. These products have the potential to function as sustainable aviation fuels (SAF), for which there is a very large, currently unmet market.

Natural photosynthesis converts solar energy into chemical bond energy stored as biomass, with efficiencies below 1% in most terrestrial plants. This rate is incompatible with the decarbonization demands of a post-industrial society. To overcome this constraint, we present a fully integrated electro-microbial CO₂ conversion (EMC2) platform that bypasses the kinetic limitations of Rubisco-based carbon fixation by coupling electrocatalytic CO₂ reduction (CO₂RR) with engineered microbial bioconversion.
The EMC2 strategy centers on soluble C2 intermediates (i.e., acetate and ethanol) as molecular bridges between the chemical and biological domains. Compared to C1 intermediates (i.e., formate and methanol) or hydrogen, C2 compounds offer faster mass transfer, higher energy and electron density, lower cellular toxicity, and broader compatibility with primary metabolic pathways. To fully exploit these advantages, we pursued a multi-layer design strategy spanning electrocatalysis, the chem-bio interface, and synthetic biology.
On the electrochemical side, we systematically engineered electrolyte composition, electrode architecture, electrolyser configuration, and catalyst design to achieve selective electrochemical reduction of carbon dioxide (CO₂ RR) to acetate and ethanol under conditions compatible with downstream biological processing. On the biological side, multi-module cellular engineering enhanced substrate utilization efficiency, reductant generation, and metabolic flux toward target products. This integrated design enabled continuous, high-productivity microbial biomass and polyhydroxyalkanoate (PHA) synthesis directly from CO₂ . Biomass productivity surpassed C1- and hydrogen-based systems by 6- and 8-fold, respectively. Our synthetic biology modules produced medium-chain-length PHAs, which are biodegradable, bio-based polymers at record productivity and chain lengths unattainable via competing electro-bio platforms. Overall, the EMC₂ system achieved 4.5% solar-to-biomass conversion efficiency, representing a multiple-fold improvement over natural photosynthesis (<1%).

We synthesized a dendritic-like Cu/Cu₂O nanocomposite using a facile electrochemical deposition method on functionalized carbon cloth. which revealed the formation of a dendritic structure nanocomposite. Similarly, electrochemical properties were also studied using cyclic voltammetry and linear sweep voltammetry. The Results demonstrated that the electrocatalyst exhibited excellent performance in the electrochemical reduction of CO₂ to ethene. Specifically, the Faradaic efficiency (FE) at a shorter deposition time (250 seconds) reached 85.63%, with 62.08% for C2 products, at a current density of 63.57 mA/cm² at -0.97 V versus RHE in H-type cells. The electrochemically active surface area was calculated to be 41.95 cm². The enhanced catalytic activity was attributed to the synergistic effects between Cu⁺ and Cu⁰, which increased the number of active sites, facilitated faster electron transfer, and improved CO₂ adsorption capacity.

Organic synthesis decisions made at the molecular level strongly influence sustainability, scalability, and end-of-life fate of polymeric materials. However, many polymer synthesis workflows remain fundamentally linear, treating purification, catalyst management, and disposal downstream challenges rather than design considerations. Here, we present a life cycle-integrated organic synthesis framework that embeds sustainability principles across monomer and initiator synthesis, copper-catalyzed polymerization, purification and regeneration.
This framework is articulated using homopolymer synthesis as a deliberately simplified proof-of-concept, enabling clear evaluation of catalyst handling, reuse, and regeneration prior to extension toward more complex polymer architectures. Photo-mediated atom transfer radical polymerization (photoATRP) is employed as a representative controlled radical polymerization strategy due to its mild conditions and low catalyst loadings; however, the underlying design principles are broadly applicable across copper-based catalytic polymerization platforms including thermal and chemically mediated ATRP variants.
Central to its approach is the intentional selection of green synthetic methodologies and reagents that support step economy, solvent compatibility, and downstream circularity. Dynamic covalent chemistry is incorporated as a molecular design principle to enable post-synthetic tunability and regeneration without full material resynthesis. Importantly, purification and catalyst management are reimagined as chemically productive steps, in which catalyst-associated streams are integrated into regeneration and reuse workflows rather than treated as waste.
By framing organic synthesis as a connected lifecycle rather than a linear sequence of reactions, this work outlines a conceptual roadmap for designing copper-catalyzed polymer systems explicitly for reuse, regeneration and reduced environmental impact, with relevance to sustainable industrial chemistry.

Pharmaceutical contaminants are increasingly detected in aquatic environments due to their widespread use, incomplete removal in conventional wastewater treatment plants, and continuous discharge into natural water bodies. Even at trace concentrations, these compounds may disrupt ecosystem balance, highlighting the need for effective remediation technologies. Advanced oxidation processes, particularly the heterogeneous photo-Fenton process, have emerged as promising alternatives for the degradation of persistent pharmaceutical contaminants.
In this study, iron-based spinel ferrites of cobalt, manganese, and copper (CoFe₂O₄, MnFe₂O₄, and CuFe₂O₄) were synthesized by coprecipitation. The materials were structurally, morphologically, and optically characterized. In addition, ferrite nanoparticles supported on graphene oxide were prepared to extend the evaluation to supported catalytic systems and different pharmaceutical compounds.
Powder X-ray diffraction (PXRD) confirmed the formation of spinel ferrite phases. Field emission scanning electron microscopy (FE-SEM) revealed quasi-spherical agglomerated morphologies, while X-ray photoelectron spectroscopy (XPS) confirmed the presence and expected oxidation states of the constituent elements at the material surfaces. Diffuse reflectance spectroscopy (DRS) was used to estimate optical band gap values through the Tauc method, yielding values in agreement with those reported for spinel ferrite photocatalysts.
The catalytic activity of the ferrites toward the degradation of pharmaceutical contaminants was evaluated under UV irradiation using the heterogeneous photo-Fenton process. Degradation strongly depended on ferrite composition, with CuFe₂O₄ showing the highest activity during the degradation of sulfamethoxazole, used as a model pharmaceutical compound, and achieving over 95% degradation after four consecutive reuse cycles. Kinetic analysis indicated apparent pseudo-first-order behavior, with higher rate constants for CuFe₂O₄ compared to CoFe₂O₄ and MnFe₂O₄. Scavenger experiments confirmed the dominant role of hydroxyl radicals, while degradation product analysis revealed the formation of short-chain carboxylic acids, indicating progressive oxidation of the pharmaceutical molecules. Preliminary experiments using real water matrices demonstrated the potential applicability of the catalytic system under more complex conditions.

Purple non-sulfur bacteria (PNSB) are promising feedstocks for wastewater treatment and bio-refinery applications. However, inefficient harvesting is a major barrier to realizing their large-scale applications. This study demonstrates that nitrogen-deficient (ND) cultivation is an effective strategy for enhancing PNSB bio-flocculation, compared with traditional nitrogen-sufficient (NS) cultivation. For both NS and ND cultures, chitosan-induced flocculation was evaluated across a range of pH values (5.0-8.0) and polymer dosages (20-300 mg/L). Under NS conditions, flocculation efficiency (F.E.) reached 71-75% under acidic pH (5.0-6.0) and declined to <50% at pH 7.0-8.0. In contrast, ND culture achieved 83-86 % F.E at pH 7.0-8.0. It corresponds to the native pH (~8.0) of both ND and NS growth media, thereby eliminating the need for chemical addition to adjust the pH. At this pH, the maximum F.E. (72%) was achieved at 100 mg/L of chitosan, whereas NS cultures required a higher dosage (200 mg/L) to reach a lower maximum F.E. (61%). In ND cultures, the zeta potential shifted from -30 to -12 mV, indicating that polymer bridging was the dominant flocculation mechanism. ND culture also showed significantly higher baseline hydrophobicity (40% vs 17% in NS), which increased to 90% at 250 mg/L of chitosan. It also found that the biomass concentration strongly influenced flocculation, with undiluted ND culture showing higher F.E. (80%), and it reduced to only 15% at 5x dilution. FTIR spectroscopy, microscopic analysis, and microbial community analysis confirmed that enhanced flocculation in ND culture was attributed to an increase in extracellular polymer substances. Thus, ND cultivation enables higher F.E. at native and near-neutral pH levels and at lower polymer dosages, demonstrating its potential to enhance the techno-economic viability of PNSB-based biorefineries

Within the framework of the Sustainable Development Goals, the replacement of fossil fuels and the mitigation of their emissions represent priority global challenges. Renewable oxygenated additives have emerged as a promising strategy to reduce atmospheric pollutants. This study presents a green synthesis route for the production of dimethyl carbonate (DMC) and diethyl carbonate (DEC) from biomethanol or bioethanol and captured carbon dioxide, applying nine principles of Green Chemistry (GC) and using Ni/Cu catalysts supported in coffee carbon grounds.
An experimental design based on green engineering was employed to evaluate the impact of these additives on the reduction of polycyclic aromatic hydrocarbons (PAHs) and soot in diesel combustion engines. The experiments were conducted in an atmospheric-pressure counterflow diffusion flame. The soot volume fraction was measured using light extinction and scattering techniques, while PAH concentrations were determined through advanced optical diagnostics such as laser-induced fluorescence and laser-induced incandescence, complemented by physicochemical characterization using NMR, FTIR, and GC.
The results revealed a differential synergistic effect: DMC promoted greater PAH formation compared to DEC under equivalent conditions, a behavior not previously reported. To further elucidate the reaction mechanisms, a kinetic–chemical model supported by computational chemistry methods was developed, incorporating PAH growth up to A7 species (seven aromatic rings, including coronene C24H12). Experimental validation confirmed that DEC was more effective than DMC in reducing soot under equivalent conditions in ethylene flames.
This work provides new evidence of how green chemistry enables the synthesis, characterization, and development of kinetic mechanisms of organic carbonates as oxygenated additives and identifies DEC as a sustainable product for emission mitigation, with prospects for technological optimization and industrial implementation aligned with environmental, economic, and social benefits.