Microbial synthesis of highly dispersed PdAu alloy for enhanced electrocatalysis

Bimetallic nanoparticles as pioneering eco-friendly catalysts for remediation of pharmaceuticals and personal care products (PPCPs)

The persistent presence of Pharmaceuticals and Personal Care Products (PPCPs) in aquatic environments poses a significant risk to both human health and ecosystems, with conventional water treatment methods often unable to effectively remove these contaminants. Recent research has identified bimetallic nanoparticles as a promising and eco-friendly solution for PPCP remediation, owing to their enhanced catalytic properties and the synergistic effects between the metals. This review critically examines the synthesis, characterization, and application of bimetallic nanoparticles for the degradation of PPCPs in water. Key synthetic approaches, particularly green synthesis methods, are explored, emphasizing their ability to control nanoparticle morphology, size, and composition. We highlight the novel catalytic mechanisms employed by bimetallic nanoparticles, including electron transfer, surface reactions, and adsorption processes, which contribute to efficient PPCP removal. Furthermore, the influence of critical factors such as nanoparticle size, composition, and surface functionalization on catalytic efficiency is analyzed. Key findings include the superior performance of bimetallic nanoparticles over monometallic counterparts, with specific emphasis on their ability to degrade a wide range of PPCPs under mild conditions. However, challenges such as scalability, stability, and environmental impact remain. This review also provides insights into the future directions for bimetallic nanoparticle development, stressing the importance of interdisciplinary research and collaborative efforts to optimize their design for large-scale, sustainable water treatment applications. Overall, this work offers a comprehensive understanding of how bimetallic nanoparticles can be optimized for sustainable water treatment solutions, highlighting their potential to mitigate the adverse effects of PPCPs on both ecosystems and public health.

Mapping Surface and Subsurface Atomic Structures of Au@Pd Core-Shell Nanoparticles in Three Dimensions

Three-dimensional (3D) atomic arrangements in the surface and subsurface parts of nanomaterials are crucial for understanding their structure-functionality correlations. However, unveiling the required structure at such a resolution remains a challenge due to the lack of effective imaging and reconstruction techniques. Here, we determine the 3D atomic surface and subsurface structures of Au@Pd core-shell nanoparticles and study their correlations with electronic and surface chemical properties using atomic-resolution electron tomography (AET). We find that the intermixing of Au and Pd is the key factor that influences the surface and subsurface structure and quantitatively reveals its negative correlations with bond disorder and tensile strain. By applying spectroscopic and electrochemical measurements, we confirm that different surface structures modify the electronic and chemical properties at different Au/Pd ratios. These results not only shed light on the complex surface and subsurface structures of realistic nanomaterials but also deepen our understanding of structure-functionality correlations in nanostructures at the single-atom level.

Biofunctional photoelectrochemical/electrochemical immunosensor based on BiVO4/BiOI-MWCNTs and Au@PdPt for alpha-fetoprotein detection

A biofunctional immunosensor combining photoelectrochemical (PEC) and electrochemical (EC) was proposed for the quantitative detection of the liver cancer marker alpha-fetoprotein (AFP) in human blood. BiVO4/BiOI-MWCNTs photoactive materials were first prepared on conductive glass FTO, and the photoelectrode was functionalized by chitosan and glutaraldehyde. Then, the AFP capture antibody (Ab1) was successfully modified on the photoelectrode, and the label-free rapid detection of AFP antigen was achieved by PEC. In addition, Au@PdPt nanospheres were also used as a marker for binding to AFP detection antibody (Ab2). Due to the excellent catalytic properties of Au@PdPt in EC reaction, a signal increase in the EC response can be achieved when Ab2 binds to the AFP antigen, which ensures high sensitivity for the detection of AFP. The detection limits of PEC and EC are 0.050 pg/mL and 0.014 pg/mL, respectively. The sensor also possesses good specificity, stability and reproducibility, shows excellent performance in the detection of clinical samples and has good clinical applicability.

Cryomicroneedle delivery of nanogold-engineered Rhodospirillum rubrum for photochemical transformation and tumor optical biotherapy

Tumor metabolite regulation is intricately linked to cancer progression. Because lactate is a characteristic metabolite of the tumor microenvironment (TME), it supports tumor progression and drives immunosuppression. In this study, we presented a strategy for antitumor therapy by developing a nanogold-engineered Rhodospirillum rubrum (R.r-Au) that consumed lactate and produced hydrogen for optical biotherapy. We leveraged a cryogenic micromolding approach to construct a transdermal therapeutic cryomicroneedles (CryoMNs) patch integrated with R.r-Au to efficiently deliver living bacterial drugs. Our long-term storage studies revealed that the viability of R.r-Au in CryoMNs remained above 90%. We found that the CryoMNs patch was mechanically strong and could be inserted into mouse skin. In addition, it rapidly dissolved after administering bacterial drugs and did not produce by-products. Under laser irradiation, R.r-Au effectively enhanced electron transfer through Au NPs actuation into the photosynthetic system of R. rubrum and enlarged lactate consumption and hydrogen production, thus leading to an improved tumor immune activation. Our study demonstrated the potential of CryoMNs-R.r-Au patch as a minimally invasive in situ delivery approach for living bacterial drugs. This research opens up new avenues for nanoengineering bacteria to transform tumor metabolites into effective substances for tumor optical biotherapy.

One-pot synthesis of 3D surface-wrinkled PdAu nanospheres for robust alcohols electrocatalysis

Three dimensional (3D) noble-metal nanomaterials with special surface structures have been regarded as high-performance catalysts for alcohol oxidation on account of their superior thermal stability, electrical conductivity and large specific surface area. Although extensive efforts have been devoted to the preparation of 3D Pd-based catalysts with superior activity and stability, designing a simple, effective and eco-friendly method remains a challenge. Herein, we developed a facile one-step coreduction strategy to synthesize a series of 3D surface-wrinkled PdAu nanospheres (NSs) with tunable Pd/Au atomic ratios and found a universal method to prepare surface-wrinkled PdM (M = Au, Pt, Cu and Pb) NSs. Benefiting from the function of the surfactant cetyltrimethylammonium chloride (CTAC), the synthesized PdAu NSs with different composition possess abundant surface wrinkles, which is beneficial for exposing more electroactive centers. Attributed to the unique geometric morphology and optimized atomic ratio, the PdAu-2 NSs exhibited an optimal mass activity (MA) of 8103 mA mg-1 and 5113 mA mg-1 for the ethylene glycol oxidation reaction (EGOR) and ethanol oxidation reaction (EOR), which was 6.1 and 4.1 times that of commercial Pd/C, respectively. Moreover, the PdAu-2 NSs exhibited superb stability after long-term current-time (i-t) and cyclic voltammetry (CV) tests of the EGOR and EOR. This work not only provides new avenues to engineer PdAu NSs with enhanced electrocatalytic performance but also offers guidance for extending to more 3D PdM (M = other metals) NSs with novel morphology applied to fuel cell fields.

Electroactive Microorganisms in Advanced Energy Technologies

Large-scale production of green and pollution-free materials is crucial for deploying sustainable clean energy. Currently, the fabrication of traditional energy materials involves complex technological conditions and high costs, which significantly limits their broad application in the industry. Microorganisms involved in energy production have the advantages of inexpensive production and safe process and can minimize the problem of chemical reagents in environmental pollution. This paper reviews the mechanisms of electron transport, redox, metabolism, structure, and composition of electroactive microorganisms in synthesizing energy materials. It then discusses and summarizes the applications of microbial energy materials in electrocatalytic systems, sensors, and power generation devices. Lastly, the research progress and existing challenges for electroactive microorganisms in the energy and environment sectors described herein provide a theoretical basis for exploring the future application of electroactive microorganisms in energy materials.

Microbial synthesis of Prussian blue for potentiating checkpoint blockade immunotherapy

Cancer immunotherapy is revolutionizing oncology. The marriage of nanotechnology and immunotherapy offers a great opportunity to amplify antitumor immune response in a safe and effective manner. Here, electrochemically active Shewanella oneidensis MR-1 can be applied to produce FDA-approved Prussian blue nanoparticles on a large-scale. We present a mitochondria-targeting nanoplatform, MiBaMc, which consists of Prussian blue decorated bacteria membrane fragments having further modifications with chlorin e6 and triphenylphosphine. We find that MiBaMc specifically targets mitochondria and induces amplified photo-damages and immunogenic cell death of tumor cells under light irradiation. The released tumor antigens subsequently promote the maturation of dendritic cells in tumor-draining lymph nodes, eliciting T cell-mediated immune response. In two tumor-bearing mouse models using female mice, MiBaMc triggered phototherapy synergizes with anti-PDL1 blocking antibody for enhanced tumor inhibition. Collectively, the present study demonstrates biological precipitation synthetic strategy of targeted nanoparticles holds great potential for the preparation of microbial membrane-based nanoplatforms to boost antitumor immunity.

Chemically engineering cells for precision medicine

Cell-based therapy holds great potential to address unmet medical needs and revolutionize the healthcare industry, as demonstrated by several therapeutics such as CAR-T cell therapy and stem cell transplantation that have achieved great success clinically. Nevertheless, natural cells are often restricted by their unsatisfactory in vivo trafficking and lack of therapeutic payloads. Chemical engineering offers a cost-effective, easy-to-implement engineering tool that allows for strengthening the inherent favorable features of cells and confers them new functionalities. Moreover, in accordance with the trend of precision medicine, leveraging chemical engineering tools to tailor cells to accommodate patients individual needs has become important for the development of cell-based treatment modalities. This review presents a comprehensive summary of the currently available chemically engineered tools, introduces their application in advanced diagnosis and precision therapy, and discusses the current challenges and future opportunities.

Leveraging Pd(100)/SnO2 interfaces for highly efficient electrochemical formic acid oxidation

The electrocatalytic formic acid oxidation (FAO) is the crucial anodic reaction of direct formic acid fuel cells (DFAFCs), but its activity remains to be largely improved in order to be practically viable. The rational development of enhanced catalysts requires thorough consideration of various contributing factors that are possibly integrated in composite systems. Here, we demonstrate that, Pd(100)/SnO₂ interfaces, provided being efficiently exploited, can significantly boost FAO activity by a factor of ∼10, compared with pure Pd(100) facets, with the mass activity reaching a record of 14.55 A mg_Pd^-1 at a 40 mV-lower peak potential. Unique Pd/SnO₂ nanocomposites with a myriad of Pd(100)/SnO₂ interfaces were obtained by a newly developed successive seeded growth strategy, wherein pre-formed SnO₂ nanospheres are used as seeds for two-round overgrowth of multitudinous Pd nanocubes. Using electron microscopic, electrochemical, spectroscopic and computational analyses, we found that the Pd(100)/SnO₂ interfaces induce lattice contraction and electron loss on Pd nanocubes, which optimize intermediate binding during FAO. Moreover, we showed that the good cubicity of the Pd nanocubes and the presence of SnO₂ nearby further promote the activity by facilitating the potential-determining step and the elimination of the poisoning CO intermediate, respectively. As such, the combined high intrinsic activity and number density of Pd(100)/SnO₂ interfaces enabled the superior activity of the Pd/SnO₂ nanocomposites. The composite material presented here holds promise for application in DFAFCs, but equally importantly, the insights regarding the structure-performance relationship would be beneficial for designing efficient metal/oxide composite catalysts for diverse electro- and photo-catalytic reactions.

Directing the Architecture of Surface-Clean Cu2O for CO Electroreduction

Tailoring the morphology of nanocrystals is a promising way to enhance their catalytic performance. In most previous shape-controlled synthesis strategies, surfactants are inevitable due to their capability to stabilize different facets. However, the adsorbed surfactants block the intrinsic active sites of the nanocrystals, reducing their catalytic performance. For now, strategies to control the morphology without surfactants are still limited but necessary. Herein, a facile surfactant-free synthesis method is developed to regulate the morphology of Cu₂O nanocrystals (e.g., solid nanocube, concave nanocube, cubic framework, branching nanocube, branching concave nanocube, and branching cubic framework) to enhance the electrocatalytic performance for the conversion of CO to n-propanol. Specifically, the Cu₂O branching cubic framework (BCF-Cu₂O), which is difficult to fabricate using previous surfactant-free methods, is fabricated by combining the concentration depletion effect and the oxidation etching process. More significantly, the BCF-Cu₂O-derived catalyst (BCF) presents the highest n-propanol current density (-0.85 mA cm^-2) at -0.45 V versus the reversible hydrogen electrode (V_RHE), which is fivefold higher than that of the surfactant-coated Cu₂O nanocube-derived catalyst (SFC, -0.17 mA cm^-2). In terms of the n-propanol Faradaic efficiency in CO electroreduction, that of the BCF exhibits a 41% increase at -0.45 V_RHE as compared with SFC. The high catalytic activity of the BCF that results from the clean surface and the coexistence of Cu(100) and Cu(110) in the lattice is well-supported by density functional theory calculations. Thus, this work presents an important paradigm for the facile fabrication of surface-clean nanocrystals with an enhanced application performance.

Synthesis and Structure of a Two-Dimensional Palladium Oxide Network on Reduced Graphene Oxide

New nanostructures often reflect new and exciting properties. Here, we present an two-dimensional, hitherto unreported PdO square network with lateral dimensions up to hundreds of nanometers growing on reduced graphene oxide (rGO), forming a hybrid nanofilm. An intermediate state of dissolved Pd(0) in the bacterium S. oneidensis MR-1 is pivotal in the biosynthesis and inspires an abiotic synthesis. The PdO network shows a lattice spacing of 0.5 nm and a thickness of 1.8 nm on both sides of an rGO layer and is proposed to be cubic or tetragonal crystal, as confirmed by structural simulations. A 2D silver oxide analog with a similar structure is also obtained using an analogous abiotic synthesis. Our study thus opens a simple route to a whole new class of 2D metal oxides on rGO as promising candidates for graphene superlattices with unexplored properties and potential applications for example in electronics, sensing, and energy conversion.

Photocatalyst-mineralized biofilms as living bio-abiotic interfaces for single enzyme to whole-cell photocatalytic applications

There is an increasing trend of combining living cells with inorganic semiconductors to construct semi-artificial photosynthesis systems. Creating a robust and benign bio-abiotic interface is key to the success of such solar-to-chemical conversions but often faces a variety of challenges, including biocompatibility and the susceptibility of cell membrane to high-energy damage arising from direct interfacial contact. Here, we report living mineralized biofilms as an ultrastable and biocompatible bio-abiotic interface to implement single enzyme to whole-cell photocatalytic applications. These photocatalyst-mineralized biofilms exhibited efficient photoelectrical responses and were further exploited for diverse photocatalytic reaction systems including a whole-cell photocatalytic CO2 reduction system enabled by the same biofilm-producing strain. Segregated from the extracellularly mineralized semiconductors, the bacteria remained alive even after 5 cycles of photocatalytic NADH regeneration reactions, and the biofilms could be easily regenerated. Our work thus demonstrates the construction of biocompatible interfaces using biofilm matrices and establishes proof of concept for future sustainable photocatalytic applications.

Biotechnological synthesis of Pd-based nanoparticle catalysts

Palladium metal nanoparticles are excellent catalysts used industrially for reactions such as hydrogenation and Heck and Suzuki C-C coupling reactions. However, the global demand for Pd far exceeds global supply, therefore the sustainable use and recycling of Pd is vital. Conventional chemical synthesis routes of Pd metal nanoparticles do not meet sustainability targets due to the use of toxic chemicals, such as organic solvents and capping agents. Microbes are capable of bioreducing soluble high oxidation state metal ions to form metal nanoparticles at ambient temperature and pressure, without the need for toxic chemicals. Microbes can also reduce metal from waste solutions, revalorising these waste streams and allowing the reuse of precious metals. Pd nanoparticles supported on microbial cells (bio-Pd) can catalyse a wide array of reactions, even outperforming commercial heterogeneous Pd catalysts in several studies. However, to be considered a viable commercial option, the intrinsic activity and selectivity of bio-Pd must be enhanced. Many types of microorganisms can produce bio-Pd, although most studies so far have been performed using bacteria, with metal reduction mediated by hydrogenase or formate dehydrogenase enzymes. Dissimilatory metal-reducing bacteria (DMRB) possess additional enzymes adapted for extracellular electron transport that potentially offer greater control over the properties of the nanoparticles produced. A recent and important addition to the field are bio-bimetallic nanoparticles, which significantly enhance the catalytic properties of bio-Pd. In addition, systems biology can integrate bio-Pd into biocatalytic processes, and processing techniques may enhance the catalytic properties further, such as incorporating additional functional nanomaterials. This review aims to highlight aspects of enzymatic metal reduction processes that can be bioengineered to control the size, shape, and cellular location of bio-Pd in order to optimise its catalytic properties.

Precise Chemodynamic Therapy of Cancer by Trifunctional Bacterium-Based Nanozymes

Chemodynamic therapy (CDT) destroys cancer cells by converting H₂O₂ or O₂ into reactive oxygen species (ROS), but its therapeutic efficacy is restricted by the antioxidant capacity of tumor. Previous solutions focused on strengthening the nanodrugs with the ability to increase ROS production or weaken the antioxidant capacity of cancer cells. Conversely, we here develop a mild nanodrug with negligible side effects. Specifically, the Au@Pt nanozyme decorated on a bacterial surface (Bac-Au@Pt) is reported to achieve precise CDT. Due to the tumor targeting ability of bacteria and catalytic property of Au@Pt nanozyme under acidic conditions, this nanosystem can release ROS to tumor cells effectively. In addition, the interferon gamma released by T cells specifically decreases the intracellular reductants in tumor cells, while having no obvious effect on normal cells. Therefore, a low dose of Bac-Au@Pt achieves a satisfactory therapeutic efficacy to tumor cells and is nontoxic to normal cells even at their acidic components. This nanosystem enables CDT and immunotherapy to mutually benefit and improve by each other, providing a promising strategy to achieve high anticancer efficacy even with a low dose usage.

Exploring the Biological Effect of Biosynthesized Au-Pd Core-Shell Nanoparticles through an Untargeted Metabolomics Approach

The biosynthesis of Au-Pd core-shell nanoparticles (NPs) with wild-type Escherichia coli (Au-Pd/E. coli) is an excellent newly established, environmentally friendly synthetic method for the fabrication of nanomaterials compared to traditional chemosynthesis. However, there is insufficient detailed bioinformation on the compatibility, metabolic process, and mechanism of this approach. Metabolomics approaches have provided an excellent alternative to numerous bioinformatics approaches for shedding light on the biological response of an organism exposed to external stimuli at the molecular level. In this study, two different doses (8 and 80 μg/mL) of Au-Pd/E. coli were applied to treat human umbilical vein endothelial cells (HUVECs). Gas chromatography/mass spectrometry coupled with bioinformatics was used to analyze the changes in the HUVEC metabolome after treatment. The results indicated the occurrence of nonsignificant acute cytotoxicity based on cell proliferation and apoptosis analysis, while high concentrations (80 μg/mL) of Au-Pd/E. coli induced dramatic changes in energy metabolism, revealing a notable inhibition of the tricarboxylic acid (TCA) cycle along with the enhancement of glycolysis, the pentose phosphate pathway, fatty acid biosynthesis, and lipid accumulation, which was correlated with mitochondrial dysfunction. The metabolomics results obtained for this novel Au-Pd/E. coli-cell system could broaden our knowledge of the biological effect of Au-Pd/E. coli and possibly reveal material modifications and technological innovations.

Microbial synthesis of efficient palladium electrocatalyst with high loadings for oxygen reduction reaction in acidic medium

Whereas limited amount of precious metal adsorbed by bacteria conflicting the needs of high loadings for better catalytic performances, cell disruption technology was adopted to smash Shewanella cells in this work, releasing abundant oxygen functional groups inside the cells for better adsorption of palladium ion. Then palladium catalysts were synthesized in two ways: 1) Pd catalyst supported on carbonized-broken-bacterial (Pd/FHNC) was obtained after direct carbonization and reduction; 2) Electrospinning technology was used to spin the broken Shewanella into fibers, and Pd nanoparticles supported on nitrogen-doped carbon nanofiber (Pd/NCNF) was prepared following carbonization and hydrogen reduction. The as-prepared catalysts exhibit excellent oxygen reduction reaction (ORR) electrocatalytic performance in the acid medium. The mass specific activities at 0.7 V of Pd/FHNC and Pd/NCNF were 0.213 A mg^-1 and 0.121 A mg^-1 which were 5.92 and 3.36 times than those of commercial Pd/C(0.036 A mg^-1) respectively, and they also displayed higher stability than Pd/C. Furthermore, the Pd loadings of Pd/FHNC and Pd/NCNF were 21.52% and 17.13% respectively. An explanation for the improved performance is the co-doping of nitrogen and phosphorus, also the tight integration of Pd and broken-bacterial. Herein, we propose a novel and effective method for synthesis of ORR electrocatalysts.

Regulating the synthesis rate and yield of bio-assembled FeS nanoparticles for efficient cancer therapy

Biosynthesis has gained growing interest due to its energy efficiency and environmentally benign nature. Recently, biogenic iron sulfide nanoparticles (FeS NPs) have exhibited excellent performance in environmental remediation and energy recovery applications. However, their biosynthesis regulation strategy and application prospects in the biomedical field remain to be explored. Herein, biogenic FeS NPs are controllably synthesized by Shewanella oneidensis MR-1 and applied for cancer therapy. Tuning the synthesis rate and yield of biogenic FeS NPs is realized by altering the initial iron precursor dosage. Notably, increasing the precursor concentration decreases and delays FeS NP biosynthesis. The biogenic FeS NPs (30 nm) are homogeneously anchored on the cell surface of S. oneidensis MR-1. Moreover, the good hydrophilic nature and outstanding Fenton properties of the as-prepared FeS NPs endow them with good cancer therapy performance. The intracellular location of the FeS NPs taken up is visualized with a soft X-ray microscope (SXM). Highly efficient cancer cell killing can be achieved at extremely low concentrations (<12 μg mL^-1), lower than those in reported works. Such good performance is attributed to the Fe²⁺ release, elevated ROS, reduced glutathione (GSH) consumption, and lipid hydroperoxide (LPO) generation. The resulting FeS NPs show excellent in vivo therapeutic performance. This work provides a facile, eco-friendly, and scalable approach to produce nanomedicine, demonstrating the potential of biogenic nanoparticles for use in cancer therapy.

Robust Colloidal Synthesis of Palladium-Gold Alloy Nanoparticles for Hydrogen Sensing

Metal nanoparticles are currently used in a variety of applications, ranging from life sciences to nanoelectronic devices to gas sensors. In particular, the use of palladium nanoparticles is gaining increasing attention due to their ability to catalyze the rapid dissociation of hydrogen, which leads to an excellent response in hydrogen-sensing applications. However, current palladium-nanoparticle-based sensors are hindered by the presence of hysteresis upon hydride formation and decomposition, as this hysteresis limits sensor accuracy. Here, we present a robust colloidal synthesis for palladium-gold alloy nanoparticles and demonstrate their hysteresis-free response when used for hydrogen detection. The obtained colloidal particles, synthesized in an aqueous, room-temperature environment, can be tailored to a variety of applications through changing the size, ratio of metals, and surface stabilization. In particular, the variation of the viscosity of the mixture during synthesis resulted in a highly tunable size distribution and contributed to a significant improvement in size dispersity compared to the state-of-the-art methods.

Photoelectric Bacteria Enhance the In Situ Production of Tetrodotoxin for Antitumor Therapy

Engineered bacteria are promising bioagents to synthesize antitumor drugs at tumor sites with the advantages of avoiding drug leakage and degradation during delivery. Here, we report an optically controlled material-assisted microbial system by biosynthesizing gold nanoparticles (AuNPs) on the surface of Shewanella algae K3259 (S. algae) to obtain Bac@Au. Leveraging the dual directional electron transport mechanism of S. algae, the hybrid biosystem enhances in situ synthesis of antineoplastic tetrodotoxin (TTX) for a promising antitumor effect. Because of tumor hypoxia-targeting feature of facultative anaerobic S. algae, Bac@Au selectively target and colonize at tumor. Upon light irradiation, photoelectrons produced by AuNPs deposited on bacterial surface are transferred into bacterial cytoplasm and participate in accelerated cell metabolism to increase the production of TTX for antitumor therapy. The optically controlled material-assisted microbial system enhances the efficiency of bacterial drug synthesis in situ and provides an antitumor strategy that could broaden conventional therapy boundaries.

General Synthesis of Amorphous PdM (M = Cu, Fe, Co, Ni) Alloy Nanowires for Boosting HCOOH Dehydrogenation

Noble metal-based nanomaterials with amorphous structures are promising candidates for developing efficient electrocatalysts. However, their synthesis remains a significant challenge, especially under mild conditions. In this paper, we report a general strategy for preparing amorphous PdM nanowires (a-PdM NWs, M = Fe, Co, Ni, and Cu) at low temperatures by exploiting glassy non-noble metal (M) nuclei generated by special ligand adsorption as the amorphization dictator. When evaluated as electrocatalysts toward formic acid oxidation, a-PdCu NWs can deliver the mass and specific activities as high as 2.93 A/mg_Pd and 5.33 mA/cm², respectively; these are the highest values for PdCu-based catalysts reported thus far, far surpassing the crystalline-dominant counterparts and commercial Pd/C. Theoretical calculations suggest that the outstanding catalytic performance of a-PdCu NWs arises from the amorphization-induced high surface reactivity, which can efficiently activate the chemically stable C-H bond and thereby significantly facilitate the dissociation of HCOOH.

Bacterial extracellular electron transfer: a powerful route to the green biosynthesis of inorganic nanomaterials for multifunctional applications

Synthesis of inorganic nanomaterials such as metal nanoparticles (MNPs) using various biological entities as smart nanofactories has emerged as one of the foremost scientific endeavors in recent years. The biosynthesis process is environmentally friendly, cost-effective and easy to be scaled up, and can also bring neat features to products such as high dispersity and biocompatibility. However, the biomanufacturing of inorganic nanomaterials is still at the trial-and-error stage due to the lack of understanding for underlying mechanism. Dissimilatory metal reduction bacteria, especially Shewanella and Geobacter species, possess peculiar extracellular electron transfer (EET) features, through which the bacteria can pump electrons out of their cells to drive extracellular reduction reactions, and have thus exhibited distinct advantages in controllable and tailorable fabrication of inorganic nanomaterials including MNPs and graphene. Our aim is to present a critical review of recent state-of-the-art advances in inorganic biosynthesis methodologies based on bacterial EET using Shewanella and Geobacter species as typical strains. We begin with a brief introduction about bacterial EET mechanism, followed by reviewing key examples from literatures that exemplify the powerful activities of EET-enabled biosynthesis routes towards the production of a series of inorganic nanomaterials and place a special emphasis on rationally tailoring the structures and properties of products through the fine control of EET pathways. The application prospects of biogenic nanomaterials are then highlighted in multiple fields of (bio-) energy conversion, remediation of organic pollutants and toxic metals, and biomedicine. A summary and outlook are given with discussion on challenges of bio-manufacturing with well-defined controllability.

Construction of stable bio-Pd catalysts for environmental pollutant remediation

It has been reported that Pd nanoparticles were a little weak to bind to the dried microbial (yeast) surface, leading to the poor stability of the bio-supported catalysts. The objectives of the study are to construct stable Pd nanocatalysts supported on the dried yeast surface with the help of a tiny amount (<0.1 wt%) of reduced graphene oxide (Pd/yeast/rGO) and apply the catalysts in environmental pollutant remediation. The characterizations of the as-obtained Pd/yeast/rGO catalysts showed that reduced GO could cover Pd/yeast materials and prepare 15–21 nm Pd nanoparticles under acid and base media. The catalytic performance of the Pd/yeast/rGO catalyst was compared with that of control Pd/yeast catalysts without GO. The results revealed the kinetic constant K_app in the reduction of 4-nitrophenol of Pd/yeast/rGO catalysts could reach 3.6 × 10⁻² s⁻¹ without stirring during the reaction, which was 2.4 times higher than that of Pd/yeast catalysts, and the Pd/yeast/rGO catalysts kept a good stability even after being reused in seven cycles. Furthermore, the catalysts also showed quite good catalytic activities on CO oxidation and decolorization of dye methylene blue (MB). Thus, Pd/yeast/rGO catalysts were proven to be highly active and stable for environmental remediation and have the advantage that they can prevent the loss of noble metals and be prepared conveniently from discarded microorganisms.

Stable bio-supported Pd/yeast/rGO catalysts were prepared by covering with a tiny amount (<0.1 wt%) of GO based on a non-enzyme reduction method.

Enhanced Formic Acid Oxidation over SnO2-decorated Pd Nanocubes

The formic acid oxidation reaction (FAOR) is one of the key reactions that can be used at the anode of low-temperature liquid fuel cells. To allow the knowledge-driven development of improved catalysts, it is necessary to deeply understand the fundamental aspects of the FAOR, which can be ideally achieved by investigating highly active model catalysts. Here, we studied SnO₂-decorated Pd nanocubes (NCs) exhibiting excellent electrocatalytic performance for formic acid oxidation in acidic medium with a SnO₂ promotion that boosts the catalytic activity by a factor of 5.8, compared to pure Pd NCs, exhibiting values of 2.46 A mg^-1 _Pd for SnO₂@Pd NCs versus 0.42 A mg^-1 _Pd for the Pd NCs and a 100 mV lower peak potential. By using ex situ, quasi in situ, and operando spectroscopic and microscopic methods (namely, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine-structure spectroscopy), we identified that the initially well-defined SnO₂-decorated Pd nanocubes maintain their structure and composition throughout FAOR. In situ Fourier-transformed infrared spectroscopy revealed a weaker CO adsorption site in the case of the SnO₂-decorated Pd NCs, compared to the monometallic Pd NCs, enabling a bifunctional reaction mechanism. Therein, SnO₂ provides oxygen species to the Pd surface at low overpotentials, promoting the oxidation of the poisoning CO intermediate and, thus, improving the catalytic performance of Pd. Our SnO _x -decorated Pd nanocubes allowed deeper insight into the mechanism of FAOR and hold promise for possible applications in direct formic acid fuel cells.

Insight into the electrocatalytic performance of in-situ fabricated electroactive biofilm-Pd: The role of biofilm thickness, initial Pd(II) concentration and the exposure time to Pd precursor

Biogenic palladium (bio-Pd) nanoparticles have been considered as promising biocatalyst for energy generation and contaminants remediation in water and sediment. Recently, an electroactive biofilm-Pd (EAB-Pd) network, which can be used directly as electrocatalyst and show enhanced electrocatalytic performance, has exhibited tremendous application potential. However, the information regarding to the controllable biosynthetic process and corresponding catalytic properties is scarce. This study demonstrated that the catalytic performance of EAB-Pd could be influenced by Pd loading on bacteria cells (Pd/cells), which was crucial to determine the final distribution characteristic of Pd nanocrystal on EAB skeleton. For instance, the high Pd/cells (over 0.18 pg cell^-1) exhibited almost 6-fold and 1.5-fold enhancement over EAB-Pds with Pd/cells below 0.03 in catalytic current toward hydrogen evolution reaction and nitrobenzene reduction, respectively. In addition, the Pd/cells was found to be affected by the synthesis factors, such as the ratio of biomass to initial Pd(II) concentration (cells/Pd_II) and the exposure time of EAB to Pd(II) precursor solution. The Pd/cells increased significantly as the cell/Pd_II ratio decreased from ~5.5 × 10⁷ to ~1.3 × 10⁷ cells L mg^-1 or the prolongation of exposure time from 3 h to 24 h. The findings developed in this work extensively expand our knowledge for the in-situ designing biogenic electrocatalyst and provide important information for the development of its catalytic property.

Biogenic Hybrid Nanosheets Activated Photothermal Therapy and Promoted Anti-PD-L1 Efficacy for Synergetic Antitumor Strategy

Bacteria show promise for use in the field of combination cancer therapy because of their abilities to accumulate in tumors and their roles as natural immunologic adjuvants. However, the huge size of bacteria decreases their chances of being delivered into tumor cells. Moreover, their toxins may cause systemic toxicity in living organisms. Here, we proposed a method to in situ synthesize Au nanoparticles on the surface of Escherichia coli (E. coli), followed by sonication to acquire Au nanoparticles loaded membrane nanosheets (AuMNs) for use in photothermal and combination cancer therapy. Compared to E. coli-loaded Au nanoparticles (E. coli@Au), the small size of membrane nanosheets can be successfully delivered into tumor cells. In addition, the enrichment of AuMNs in tumor site is significantly enhanced via EPR effect, facilitating to activate photothermal conversion under 808 nm laser. Besides, the function of bacteria as natural immunologic adjuvants to promote anti-PD-L1 efficacy is still retained in AuMNs, while the inflammation and damage to viscera caused by AuMNs were milder than E. coli@Au. This study aims to decrease the systemic toxicity of bacteria and promote anti-PD-L1 efficacy in bacteria-mediated combination therapy, so as to open up a new avenue for drug delivery via natural processes.

Proteins-Based Nanocatalysts for Energy Conversion Reactions

In recent years, the incorporation of molecular enzymes into nanostructured frameworks to create efficient energy conversion biomaterials has gained increasing interest as a promising strategy owing to both the dynamic behavior of proteins for their electrocatalytic function and the unique properties of the synergistic interactions between proteins and nanosized materials. Herein, we review the impact of proteins on energy conversion fields and the contribution of proteins to the improved activity of the resulting nanocomposites. We address different strategies to fabricate protein-based nanocatalysts as well as current knowledge on the structure-function relationships of enzymes during the catalytic processes. Additionally, a comprehensive review of state-of-the-art bioelectrocatalytic materials for water-splitting reactions such as hydrogen evolution reaction (HER) and oxygen evolution reactions (OER) is afforded. Finally, we briefly envision opportunities to develop a new generation of electrocatalysts towards the electrochemical reduction of N₂ to NH₃ using theoretical tools to built nature-inspired nitrogen reduction reaction catalysts.

Promoting Effects of Au Submonolayer Shells on Structure-Designed Cu-Pd/Ir Nanospheres: Greatly Enhanced Activity and Durability for Alkaline Ethanol Electro-Oxidation

Rationally engineering the surface physicochemical properties of nanomaterials can improve their activity and durability for various electrocatalytic and energy conversion applications. Cu-Pd/Ir (CPI) nanospheres (NSs) anchored on N-doped porous graphene (NPG) [(CPI NSs/NPG)] have been recently demonstrated as a promising electrocatalyst for the alkaline ethanol oxidation reaction (EOR); to further enhance their electrocatalytic performance, the NPG-supported CPI NSs are coated with Au submonolayer (SML) shells (SMSs), through which their surface physicochemical properties can be tuned. CPI NSs/NPG is prepared by our previously developed method and possesses the special structures of composition-graded Cu₁Pd₁ and surface-doped Ir_0.03. The Au SMSs with designed surface coverages are formed via an electrochemical technology involving incomplete Cu underpotential deposition (UPD) and Au³⁺ galvanic replacement. A distinctive volcano-type relation between the EOR electrocatalytic activity and the Au-SMS surface coverage for CPI@Au_SML NSs/NPG is revealed, and the optimal CPI@Au_1/6ML NSs/NPG greatly surpasses commercial Pd/C and CPI NSs/NPG in electrocatalytic activity and noble metal utilization. More importantly, its electrocatalytic durability in 1 h chronoamperometric and 500-cycle potential cycling degradation tests is also significantly improved. According to detailed physicochemical characterizations, electrochemical analyses, and density functional theory calculations, the promoting effects of the Au SMS for enhancing the EOR electrocatalytic activity and durability of CPI NSs/NPG can be mainly attributed to the greatly weakened carbonaceous intermediate bonding and properly increased surface oxidation potential. This work also proposes a versatile and effective strategy to tune the surface physicochemical properties of metal-based nanomaterials via incomplete UPD and metal-cation galvanic replacement for advancing their electrocatalytic and energy conversion performance.

Microbe-Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

Microbe-mediated mineralization is ubiquitous in nature, involving bacteria, fungi, viruses, and algae. These mineralization processes comprise calcification, silicification, and iron mineralization. The mechanisms for mineral formation include extracellular and intracellular biomineralization. The mineral precipitating capability of microbes is often harnessed for green synthesis of metal nanoparticles, which are relatively less toxic compared with those synthesized through physical or chemical methods. Microbe-mediated mineralization has important applications ranging from pollutant removal and nonreactive carriers, to other industrial and biomedical applications. Herein, the different types of microbe-mediated biomineralization that occur in nature, their mechanisms, as well as their applications are elucidated to create a backdrop for future research.

Shewanella oneidensis MR-1 self-assembled Pd-cells-rGO conductive composite for enhancing electrocatalysis

Biosynthesized noble metal nanoparticles (NPs) as promising green catalysts for electrochemical application has invited a lot of attention. However, effective electron transfer between biosynthesized NPs and electrode remains a challenge due to the uncontrollable and poor conductive property of cell substrates. In this study, graphene oxide (GO) was introduced into a bio-Pd synthesis process governed by Shewanella oneidensis MR-1, which was demonstrated to be simultaneously reduced with Pd(II) and transformed to reduced GO (rGO), resulting in the formation of a Pd-cells-rGO composite. Compared to the control without rGO (Pd-cells), the electrochemical conductivity of Pd-cells-rGO composite increased from almost zero to 196 μS cm^-1, indicating the rGO facilities the electron transport across the composite. Electrochemical characterizations revealed the electrochemical active surface area (ECSA) of Pd in Pd-cells-rGO was enlarged by increasing the amount of rGO in the composite, clearly indicating that the conductive network created by rGO enable the Pd NPs receive electrons from electrode and become electrochemical active. A considerable enhancement of electrocatalytic activity was further confirmed for Pd-cells-rGO as indicated by 36.7- and 17.2-fold increase (Pd-cells-rGO with Pd/GO ratio of 5/1 vs Pd-cells) of steady state current density toward hydrogen evolution and nitrobenzene reduction at -0.7 V and -0.55 V vs Ag/AgCl, respectively. We also compared the electrocatalytic performance with MWCNTs hybrids Pd-cells-CNTs. It was found that the association of Pd, cells and rGO creates an interactive and synergistic environment to allow higher conductivity and catalytic activity under the same amount of carbon nanomaterial. The strategy developed in this work activates a highly reactive NPs and proposed a designable protocol for enhancing electrocatalytic activity of biocatalysts.

CaO-Promoted Graphene-Supported Palladium Nanocrystals as a Universal Electrocatalyst for Direct Liquid Fuel Cells

Here, we present the fabrication of a reduced graphene oxide-supported PdCa (PdCa/rGO) alloyed catalyst via a NaBH₄ reduction method for direct alcohol fuel cells in basic medium and direct formic acid fuel cells in acidic medium. Powder X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, inductively coupled plasma mass spectrometry, and Raman spectroscopy are used to characterize the PdCa/rGO catalyst. We proved that the calcium oxide significantly enhances the electrocatalytic methanol, ethanol, and formic acid oxidation over the Pd/rGO surface. The obtained mass activities for PdCa/rGO are 4838.06, 4674.70, and 3906.49 mA mg^-1 for formic acid, methanol, and ethanol, respectively. Long-term stability, high activity, and high level of tolerance to CO poisoning of the PdCa/rGO electrocatalyst are attributed to the presence of calcium oxide. These results prove that the PdCa/rGO catalyst has improved electrocatalytic performance for the oxidation of formic acid, methanol, and ethanol with reference to the Pd/rGO.

Bacteria-Assisted Synthesis of Nanosheet-Assembled TiO2 Hierarchical Architectures for Constructing TiO2-Based Composites for Photocatalytic and Electrocatalytic Applications

Synthesis and application of three-dimensional TiO₂ hierarchical architectures are one of the major priorities in the research and development of TiO₂ catalysts. Using bacteria as a template and a reactor, a bioinspired strategy was developed in the present study to synthesize nanosheet-assembled TiO₂ hierarchical architectures (N-TiO₂-HA) and relative composites for photocatalytic and electrocatalytic applications. In the first part of this work, three kinds of bacteria were used for the synthesis of N-TiO₂-HA with satisfactory monodispersity, and the growth mechanism was investigated. In the second part, porous TiO₂ hollow spheres (P-TiO₂-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in air, were incorporated with MIL-101(Fe) to improve the visible-light photocatalytic efficiency. The results of the photo-Fenton-assisted degradation of rhodamine B and ciprofloxacin indicate that the synthesized composites have excellent visible-light photocatalytic activity. In the third part, the nanosheet-assembled TiO₂-carbon hollow spheres (N-TiO₂-C-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in argon atmosphere, were electrodeposited with Pt for electrocatalytic oxidation of methanol. The electrochemical measurements show that Pt-deposited N-TiO₂-C-HS have better electrocatalytic activity, stability, and tolerance to CO poisoning than commercial Pt/C catalysts.

Bi(OH)3/PdBi Composite Nanochains as Highly Active and Durable Electrocatalysts for Ethanol Oxidation

Developing high-performance electrocatalysts for the ethanol oxidation reaction (EOR) is critical to the commercialization of direct ethanol fuel cells. However, current EOR catalysts suffer from high cost, low activity, and poor durability. Here we report the preparation of PdBi-Bi(OH)₃ composite nanochains with outstanding EOR activity and durability. The incorporation of Bi can tune the electronic structure and downshift the d-band center of Pd while the surface decoration of Bi(OH)₃ can facilitate the oxidative removal of CO and other carbonaceous intermediates. As a result, the nanochains manifest an exceptional mass activity (5.30 A mg_Pd^-1, 4.6-fold higher than that of commercial Pd/C) and outstanding durability (with a retained current density of ∼1.00 A mg_Pd^-1 after operating for 20 000 s). More importantly, the nanochain catalyst can be reactivated, and negligible activity loss has been observed after operating for 200 000 s with periodic reactivation, making it one of the best EOR catalysts.

Characterization of Palladium Nanoparticles Produced by Healthy and Microwave-Injured Cells of Desulfovibrio desulfuricans and Escherichia coli

Numerous studies have focused on the bacterial synthesis of palladium nanoparticles (bio-Pd NPs), via uptake of Pd (II) ions and their enzymatically-mediated reduction to Pd (0). Cells of Desulfovibrio desulfuricans (obligate anaerobe) and Escherichia coli (facultative anaerobe, grown anaerobically) were exposed to low-dose radiofrequency (RF) radiation(microwave (MW) energy) and the biosynthesized Pd NPs were compared. Resting cells were exposed to microwave energy before Pd (II)-challenge. MW-injured Pd (II)-treated cells (and non MW-treated controls) were contacted with H2 to promote Pd(II) reduction. By using scanning transmission electron microscopy (STEM) associated with a high-angle annular dark field (HAADF) detector and energy dispersive X-ray (EDX) spectrometry, the respective Pd NPs were compared with respect to their mean sizes, size distribution, location, composition, and structure. Differences were observed following MWinjury prior to Pd(II) exposure versus uninjured controls. With D. desulfuricans the bio-Pd NPs formed post-injury showed two NP populations with different sizes and morphologies. The first, mainly periplasmically-located, showed polycrystalline Pd nano-branches with different crystal orientations and sizes ranging between 20 and 30 nm. The second NPpopulation, mainly located intracellularly, comprised single crystals with sizes between 1 and 5 nm. Bio-Pd NPs were produced mainly intracellularly by injured cells of E. coli and comprised single crystals with a size distribution between 1 and 3 nm. The polydispersity index was reduced in the bio-Pd made by injured cells of E. coli and D. desulfuricans to 32% and 39%, respectively, of the values of uninjured controls, indicating an increase in NP homogeneity of 30-40% as a result of the prior MWinjury. The observations are discussed with respect to the different locations of Pd(II)-reducing hydrogenases in the two organisms and with respect to potential implications for the catalytic activity of the produced NPs following injury-associated altered NP patterning.

Nanocatalysts for Electrocatalytic Oxidation of Ethanol

The use of ethanol as a fuel in direct alcohol fuel cells depends not only on its ease of production from renewable sources, but also on overcoming the challenges of storage and transportation. In an ethanol-based fuel cell, highly active electrocatalysts are required to break the C-C bond in ethanol for its complete oxidation at lower overpotentials, with the aim of increasing the cell performance, ethanol conversion rates, and fuel efficiency. In recent decades, the development of wet-chemistry methods has stimulated research into catalyst design, reactivity tailoring, and mechanistic investigations, and thus, created great opportunities to achieve efficient oxidation of ethanol. In this Minireview, the nanomaterials tested as electrocatalysts for the ethanol oxidation reaction in acid or alkaline environments are summarized. The focus is mainly on nanomaterials synthesized by using wet-chemistry methods, with particular attention on the relationship between the chemical and physical characteristics of the catalysts, for example, catalyst composition, morphology, structure, degree of alloying, presence of oxides or supports, and their activity for ethanol electro-oxidation. As potential alternatives to noble metals, non-noble-metal catalysts for ethanol oxidation are also briefly reviewed. Insights into further enhancing the catalytic performance through the design of efficient electrocatalysts are also provided.

Effects of Single and Mixed Energy Sources on Intracellular Nanoparticles Synthesized by Acidithiobacillus ferrooxidans

Effective biosynthesis of magnetite nanoparticles using current technology is challenging. We investigated the synthesis of nanoparticles by Acidithiobacillus ferrooxidans grown on ferrous iron, elemental sulphur, and mixtures of both substrates. A comparison of tests with different doping amounts of elemental sulphur in ferrous-containing medium showed that the addition of 0.25 and 0.5 M elemental sulphur to the medium resulted in an increased delay of microbial growth and ferrous iron oxidation. TEM suggested that the ferrous material was an essential energy source for the synthesis of nanoparticles in cells. TEM results indicated that the different ratios of ferrous and sulphur had no significant effect on the morphology of bacteria and the size of nanoparticles. High-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and X-ray absorption near edge structure (XANES) showed that the nanoparticles were composed of magnetite. For the first time, HRTEM and XANES spectra in-situ characterization was conducted to investigate the nanoparticles that were synthesized by A. ferrooxidans. The findings from this study indicated that the different ratios of ferrous and sulphur had no significant effect on size and shape of nanoparticles synthesized by A. ferrooxidans.

Microbial synthesis of Pd-Pt alloy nanoparticles using Shewanella oneidensis MR-1 with enhanced catalytic activity for nitrophenol and azo dyes reduction

Bimetallic nanoparticles (NPs) often exhibit improved catalytic performance due to the electronic and spatial structure changes. Herein, a novel green biosynthesis method for Pd-Pt alloy NPs using Shewanella oneidensis MR-1 was proposed. The morphology, size and crystal structure of Pd-Pt alloy NPs were studied by a suite of characterization techniques. Results showed Pd-Pt alloy NPs were successfully synthesized inside and outside the cell. The biosynthesized Pd-Pt alloy NPs were polycrystalline and face-centered-cubic structure with the particle size ranged from 3-40 nm. Furthermore, the catalytic experiment demonstrated that the Pd-Pt alloy NPs exhibited the highest performance for the catalytic reduction of nitrophenol and azo dyes compared with the as-synthesized Pd and Pt monometallic NPs. This enlarged catalytic activity resulted from the synergistic effect of Pd and Pt element. Thereby, this paper provided a simple biosynthesis method for producing bimetallic alloy nanocatalyst with superior activity for contaminant degradation.

Controllable conversion of Prussian blue@yeast bio-template into 3D cage-like magnetic Fe3O4@N-doped carbon absorbent and its cohesive regeneration by persulfate activation

A multitude of heteroatom-doped carbon adsorbents have been explored to cope with ever-growing organic pollution. However, development of these advanced carbon materials with adequate activity and stability remains challenging. Herein, unique 3D cage-like magnetic N-doped Fe3O4@C adsorbents were rationally constructed by a one-step pyrolysis of Prussian blue@yeast (PB@yeast) bio-templates. By using yeast as an available biological support, the prepared Fe3O4@C hybrids were demonstrated to provide a sufficient number of Fe, N and C atoms for the novel cage-like microstructures, making them a new type of Fe, N co-doped carbon absorbents with a facile preparation procedure and remarkable adsorption behavior. Rhodamine B (RhB) removal indicated that the prepared N-doped Fe3O4@C adsorbents displayed high adsorption capabilities in a near-neutral solution, and Fe3O4@C (1 : 0.11) exhibited a maximum adsorption capability of 257.06 mg g-1. More importantly, spent N-doped Fe3O4@C absorbents, which could be recovered by magnetic separation and cohesive persulfate (PS) activated photo-Fenton regeneration, showed excellent adsorption reusability and high stability even after 5 cycles. Overall, this paper presents a simple method for fabrication of a 3D cage-like magnetic N-doped Fe3O4@C adsorbent, which provides a significant guidance for the study of Fe, N co-doped carbon adsorbents towards dye wastewater treatment.

Bimetallic nanoporous Pd-Ag prepared by dealloying with polyvinylpyrrolidone and their electrocatalytic properties

Bimetallic nanoporous Pd-Ag solid solution alloys with hierarchical structure were prepared by dealloying melt-spun Al-Pd-Ag ribbons in a 10 wt% H₃PO₄ solution. Electrocatalytic properties of nanoporous Pd-Ag alloys were measured in comparison with the nanoporous Pd without Ag. Experimental results showed that the nanoporous Pd-Ag alloys displayed electrocatalytic properties superior to their Ag-free counterparts. In particular, the optimised composition was revealed to be Pd/Ag = 3/2 in atomic ratio in the precursor with fixed 85 at% Al alloys, which yielded in a peak current density in the nanoporous Pd-Ag alloy two times that of the pure Pd one. The electrocatalytic activity of nanoporous Pd-Ag alloy with refined microstructure was further increased up to three times of the pure Pd one by adding 1 mM polyvinylpyrrolidone (PVP) into the H₃PO₄ solution. The underlying mechanism of refinement was related to a restriction effect on the free diffusion of Pd and Ag under adsorption of the PVP macromolecules. The significant improvement in the electrocatalytic properties was attributed to the dual promotion by the electron transfer from PVP to Pd-Ag and by a synergistic effect between Pd and Ag.

Palladium-Cobalt Nanowires Decorated with Jagged Appearance for Efficient Methanol Electro-oxidation

Inexpensive, active, stable, and CO-tolerant nonplatinum catalysts for efficient methanol electro-oxidation are highly desirable to direct methanol fuel cell (DMFC) technology; however, it is still challenging. In this study, we report palladium and cobalt nanowires with jagged appearance (Pd-Co J-NWs), synthesized via first anodic-aluminum-oxide template-confined electrodeposition of Pd-Co regular nanowires, followed by a wet-chemical transformation. Benefiting from the "jagged" appearance and Co dopants, the mass and specific activities of Pd-Co J-NWs for methanol electro-oxidation are evaluated ∼3.2 times and ∼2.1 times as high as those of Pd/C catalysts, respectively. After chronoamperometric measurements for 2000 s, the catalytic stability of Pd-Co J-NWs is ∼5.4 times higher compared to that of commercial Pd/C. Moreover, the onset potential of CO-stripping of Pd-Co J-NWs (0.5 V) is lower than that of Pd/C (0.7 V), suggesting CO antipoisoning. Our approach to Pd-Co J-NWs catalysts provides an experimental guideline for designing other high-performance nonplatinum catalysts, which is promising for future DMFC industry.

Programming Cells for Dynamic Assembly of Inorganic Nano-Objects with Spatiotemporal Control

Programming living cells to organize inorganic nano-objects (NOs) in a spatiotemporally precise fashion would advance new techniques for creating ordered ensembles of NOs and new bio-abiotic hybrid materials with emerging functionalities. Bacterial cells often grow in cellular communities called biofilms. Here, a strategy is reported for programming dynamic biofilm formation for the synchronized assembly of discrete NOs or hetero-nanostructures on diverse interfaces in a dynamic, scalable, and hierarchical fashion. By engineering Escherichia coli to sense blue light and respond by producing biofilm curli fibers, biofilm formation is spatially controlled and the patterned NOs' assembly is simultaneously achieved. Diverse and complex fluorescent quantum dot patterns with a minimum patterning resolution of 100 µm are demonstrated. By temporally controlling the sequential addition of NOs into the culture, multilayered heterostructured thin films are fabricated through autonomous layer-by-layer assembly. It is demonstrated that biologically dynamic self-assembly can be used to advance a new repertoire of nanotechnologies and materials with increasing complexity that would be otherwise challenging to produce.

Palladized cells as suspension catalyst and electrochemical catalyst for reductively degrading aromatics contaminants: Roles of Pd size and distribution

The palladized cell (Pd-cell) could be used as an efficient catalyst in catalyzing the degradations of a wide variety of environmental contaminants. Nevertheless, when the Pd NPs associate with the bacteria, the catalytic activity likely significantly affected by the biomass. Quantitative indicators that characterize of Pd-cell are necessary and little attention has been paid to investigate how the catalytic efficiency of Pd-cell is affected by the size and distribution of Pd NPs. To fill this gap, we explored the roles of the above-mentioned key factors on the performance of Pd-cell in catalyzing the degradations of two aromatic contaminants (nitrobenzene and p-chlorophenol) in two commonly used scenarios: (1) using Pd-cell as suspended catalyst in solution and (2) using Pd-cell as electrocatalyst directly coated on electrode. In scenario (1), the relationship of exposing area to Pd particle size and distribution factors was established. Based on theoretical estimation and catalytic performance analysis, the results indicated that adjusting the exposing area to a large value (9.3 ± 0.1 × 10⁵ nm² mg^-1 Pd) was extremely effective for improving the catalytic activity of Pd-cell used as a suspension catalyst. In scenario (2), our results showed that the best electrocatalytic performances were achieved on the electrode decorated with Pd-cells with the largest NP size (54.3 ± 16.4 nm), which exerted maximum electrochemical active surface area (10.6 m² g^-1) as well as favorable conductivity. The coverage of deposited Pd NPs (>95%) on the cell surface played a crucial role in boosting the conductivity of biocatalyst, thus determining the possibility of Pd-cell as an efficient electrocatalyst. The findings of this study provide a guidance for the synthesis and application of Pd-cell, which enables the design of Pd-cell to be suitable for different catalysis systems with high catalytic performance.

Metallic bionanocatalysts: potential applications as green catalysts and energy materials

Microbially generated or supported nanocatalysts have potential applications in green chemistry and environmental application. However, precious (and base) metals biorefined from wastes may be useful for making cheap, low-grade catalysts for clean energy production. The concept of bionanomaterials for energy applications is reviewed with respect to potential fuel cell applications, bio-catalytic upgrading of oils and manufacturing 'drop-in fuel' precursors. Cheap, effective biomaterials would facilitate progress towards dual development goals of sustainable consumption and production patterns and help to ensure access to affordable, reliable, sustainable and modern energy.

Biosynthesis of Inorganic Nanoparticles: A Fresh Look at the Control of Shape, Size and Composition

Several methodologies have been devised for the design of nanomaterials. The "Holy Grail" for materials scientists is the cost-effective, eco-friendly synthesis of nanomaterials with controlled sizes, shapes and compositions, as these features confer to the as-produced nanocrystals unique properties making them appropriate candidates for valuable bio-applications. The present review summarizes published data regarding the production of nanomaterials with special features via sustainable methodologies based on the utilization of natural bioresources. The richness of the latter, the diversity of the routes adopted and the tuned experimental parameters have led to the fabrication of nanomaterials belonging to different chemical families with appropriate compositions and displaying interesting sizes and shapes. It is expected that these outstanding findings will encourage researchers and attract newcomers to continue and extend the exploration of possibilities offered by nature and the design of innovative and safer methodologies towards the synthesis of unique nanomaterials, possessing desired features and exhibiting valuable properties that can be exploited in a profusion of fields.