skip to main content


Title: Enzymatic synthesis of supported CdS quantum dot/reduced graphene oxide photocatalysts
Photocatalysis is an attractive, sustainable, and potentially low-cost route to capture solar energy as fuel. However, current photocatalytic materials synthesis routes are not easily scaled-up to the magnitude required to impact our energy consumption due to both economic and environmental concerns. While the elements utilized are often earth abundant, typical synthetic routes utilize organic solvents at elevated temperatures with relatively expensive precursors. Herein, we demonstrate the fully biomineralized synthesis of a quantum confined CdS/reduced graphene oxide (CdS/rGO) photocatalyst catalyzed by the single enzyme cystathionine γ-lyase (CSE). The synthesis is performed at pH 9 in a buffered aqueous solution, under ambient conditions, and utilizes the low-cost precursors Cd acetate, l -cysteine, graphene oxide, and a poly- l -lysine linker molecule. CSE actively decomposes l -cysteine to generate reactive HS − in aqueous solution at pH 9. Careful selection and control of the synthesis conditions enable both reduction of graphene oxide to rGO, and control over the mean CdS nanocrystal size. The CdS is conjugated to the rGO via a poly- l -lysine crosslinker molecule introduced during rGO formation. The completed CdS/rGO photocatalyst is capable of producing H 2 , without the aid of a noble metal co-catalyst, at a rate of 550 μmol h −1 g −1 for an optimized CdS/rGO ratio. This rate is double that measured for unsupported CdS and is comparable to CdS/rGO photocatalysts produced using more typical chemical synthesis routes. Single enzyme biomineralization by CSE can produce a range of metal chalcogenides without altering the enzyme or benign approach, making this an easily adaptable procedure for the sustainable production of a wide variety of important photocatalyst systems.  more » « less
Award ID(s):
1821389
NSF-PAR ID:
10197635
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Green Chemistry
Volume:
21
Issue:
15
ISSN:
1463-9262
Page Range / eLocation ID:
4046 to 4054
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. If hydrogen evolution photocatalysis are to be deployed at industrial scale, the synthesis of these photocatalytic materials must be both economically and environmentally scalable. This suggests that we must move towards green synthesis of earth-abundant photocatalysts while also maintaining high catalytic performance. Herein, we present the enzymatically driven, aqueous phase, low temperature, synthesis of an earth-abundant nickel sulfide (Ni x S y ) hydrogen evolution cocatalyst, and its integration into a CdS/Ni x S y heterostructured photocatalyst. This resulting photocatalyst provides hydrogen evolution rates (10 500 μmol h −1 g −1 ) comparable to photocatalysts prepared by more traditional routes. Furthermore, the Ni x S y is demonstrated to provide similar activity enhancement to the more traditional, but also more expensive platinum cocatalysts. To achieve this result, we carefully studied and engineered the synthesis environment to maintain enzyme activity towards HS − production while sustaining a sufficient concentration of free Ni 2+ in solution to enable reaction and formation of Ni x S y . Ultimately, this work provides a methodology to control the coordination of metal precursors in low temperature, aqueous systems to allow for precipitation of catalytically active materials and demonstrates the viability of green synthesis pathways for photocatalysts. 
    more » « less
  2. Advances in the synthesis and processing of graphene-based materials have presented the opportunity to design novel lithium-ion battery (LIB) anode materials that can meet the power requirements of next-generation power devices. In this work, a poly(methacrylic acid) (PMAA)-induced self-assembly process was used to design super-mesoporous Fe 3 O 4 and reduced-graphene-oxide (Fe 3 O 4 @RGO) anode materials. We demonstrate the relationship between the media pH and Fe 3 O 4 @RGO nanostructure, in terms of dispersion state of PMAA-stabilized Fe 3 O 4 @GO sheets at different surrounding pH values, and porosity of the resulted Fe 3 O 4 @RGO anode. The anode shows a high surface area of 338.8 m 2 g −1 with a large amount of 10–40 nm mesopores, which facilitates the kinetics of Li-ions and electrons, and improves electrode durability. As a result, Fe 3 O 4 @RGO delivers high specific-charge capacities of 740 mA h g −1 to 200 mA h g −1 at various current densities of 0.5 A g −1 to 10 A g −1 , and an excellent capacity-retention capability even after long-term charge–discharge cycles. The PMAA-induced assembly method addresses the issue of poor dispersion of Fe 3 O 4 -coated graphene materials—which is a major impediment in the synthesis process—and provides a facile synthetic pathway for depositing Fe 3 O 4 and other metal oxide nanoparticles on highly porous RGO. 
    more » « less
  3. The importance and widespread need for accurate pH monitoring necessitates the fabrication of new pH sensors with high sensitivity that can be used in a variety of environments. However, typical pH sensors have certain limitations ( e.g. , glass electrodes are fragile and require consistent upkeep, colorimetric pH strips are single use and inaccurate). Herein, we examine the pH-response of multilayers consisting of Ti 3 C 2 T x nanosheets and polycations fabricated using layer-by-layer (LbL) assembly. The MXene sheets themselves are pH-responsive due to their hydroxyl surface groups, and this effect may be amplified with the choice of an appropriate polycation. Specifically, the performance of multilayers assembled with the strong electrolyte poly (diallyldimethylammonium) (PDADMA) or pH-sensitive branched polyethylenimine (BPEI) is compared. As expected, the use of a pH-sensitive constituent leads to a 464% increase in pH sensitivity (116 kΩ pH −1 unit vs. 25 kΩ pH −1 unit) as compared to PDADMA. This is due to the conformational changes that BPEI undergoes with (de)protonation as pH changes. Further comparisons with reduced graphene oxide (rGO), which is far less pH responsive, confirm the unique pH responsivity of MXene nanosheets themselves. The ability to enhance response to particular stimuli by changing the constituent polycation demonstrates promise for future use of MXenes in resistive sensors for a variety of stimuli. 
    more » « less
  4. “Concentrate-and-degrade” is an effective strategy to promote mass transfer and degradation of pollutants in photocatalytic systems, yet suitable and cost-effective photocatalysts are required to practice the new concept. In this study, we doped a post-transition metal of Indium (In) on a novel composite adsorptive photocatalyst, activated carbon-supported titanate nanotubes (TNTs@AC), to effectively degrade perfluorooctanoic acid (PFOA). In/TNTs@AC exhibited both excellent PFOA adsorption (>99% in 30 min) and photodegradation (>99% in 4 h) under optimal conditions (25 °C, pH 7, 1 atm, 1 g/L catalyst, 0.1 mg/L PFOA, 254 nm). The heterojunction structure of the composite facilitated a cooperative adsorption mode of PFOA, i.e., binding of the carboxylic head group of PFOA to the metal oxide and attachment of the hydrophobic tail to AC. The resulting side-on adsorption mode facilitates the electron (e‒) transfer from the carboxylic head to the photogenerated hole (h+), which was the major oxidant verified by scavenger tests. Furthermore, the presence of In enables direct electron transfer and facilitates the subsequent stepwise defluorination. Finally, In/TNTs@AC was amenable to repeated uses in four consecutive adsorption-photodegradation runs. The findings showed that adsorptive photocatalysts can be prepared by hybridization of carbon and photoactive semiconductors and the enabled “concentrate-and-degrade” strategy is promising for the removal and degradation of trace levels of PFOA from polluted waters. 
    more » « less
  5. Low-cost materials, scalable manufacturing, and high power conversion efficiency are critical enablers for large-scale applications of photovoltaic (PV) cells. Cu 2 ZnSn(S,Se) 4 (CZTSSe) has emerged as a promising PV material due to its low-cost earth-abundant nature and the low toxicity of its constituents. We present a compact and environmentally friendly route for preparing metal sulfide (metals are Cu, Zn, and Sn) nanoparticles (NPs) and optimize their annealing conditions to obtain uniform carbon-free CZTSSe thin films with large grain sizes. Further, the solution-stable binary NP inks synthesized in an aqueous solution with additives are shown to inhibit the formation of secondary phases during annealing. A laboratory-scale PV cell with a Al/AZO/ZnO/CdS/CZTSSe/Mo-glass structure is fabricated without anti-reflective coatings, and a 9.08% efficiency under AM1.5G illumination is demonstrated for the first time. The developed scalable, energy-efficient, and environmentally sustainable NP synthesis approach can enable integration of NP synthesis with emerging large-area deposition and annealing methods for scalable fabrication of CZTSSe PV cells. 
    more » « less