The Future of Material Scientists in an Age of Artificial Intelligence

Material science has historically evolved in tandem with advancements in technologies for characterization, synthesis, and computation. Another type of technology to add to this mix is machine learning (ML) and artificial intelligence (AI). Now increasingly sophisticated AI-models are seen that can solve progressively harder problems across a variety of fields. From a material science perspective, it is indisputable that machine learning and artificial intelligence offer a potent toolkit with the potential to substantially accelerate research efforts in areas such as the development and discovery of new functional materials. Less clear is how to best harness this development, what new skill sets will be required, and how it may affect established research practices. In this paper, those question are explored with respect to increasingly more sophisticated ML/AI-approaches. To structure the discussion, a conceptual framework of an AI-ladder is introduced. This AI-ladder ranges from basic data-fitting techniques to more advanced functionalities such as semi-autonomous experimentation, experimental design, knowledge generation, hypothesis formulation, and the orchestration of specialized AI modules as stepping-stones toward general artificial intelligence. This ladder metaphor provides a hierarchical framework for contemplating the opportunities, challenges, and evolving skill sets required to stay competitive in the age of artificial intelligence.

Electrochemical Doping and Structural Modulation of Conductive Metal-Organic Frameworks

In this study, we introduce an electrochemical doping strategy aimed at manipulating the structure and composition of electrically conductive metal-organic frameworks (c-MOFs). Our methodology is exemplified through a representative c-MOF, Ni3(HITP)2 (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene), synthesized into porous thin films supported by nanocellulose. While the c-MOF exhibits characteristic capacitive behavior in neutral electrolyte; it manifests redox behaviors in both acidic and alkaline electrolytes. Evidence indicates that the organic ligands within c-MOF undergo oxidation (p-doping) and reduction (n-doping) when exposed to specific electrochemical potentials in acidic and alkaline electrolyte, respectively. Interestingly, the p-doping process proves reversible, with the c-MOF structure remaining stable across cyclic p-doping/de-doping. In contrast, the n-doping is irreversible, leading to the gradual decomposition of the framework into inorganic species over a few cycles. Drawing on these findings, we showcase the versatile electrochemical applications of c-MOFs and their derived composites, encompassing electrochemical energy storage, electrocatalysis, and ultrafast actuation. This study provides profound insights into the doping of c-MOFs, offering a new avenue for modulating their chemical and electronic structure, thereby broadening their potential for diverse electrochemical applications.

Amine Gas-Induced Reversible Optical Bleaching of Bismuth-Based Lead-Free Perovskite Thin Films

Reversible optical property changes in lead-free perovskites have recently received great interest due to their potential applications in smart windows, sensors, data encryption, and various on-demand devices. However, it is challenging to achieve remarkable color changes in their thin films. Here, methylamine gas (CH3 NH2 , MA0 ) induced switchable optical bleaching of bismuth (Bi)-based perovskite films is demonstrated for the first time. By exposure to an MA0 atmosphere, the color of Cs2 AgBiBr6 (CABB) films changes from yellow to transparent, and the color of Cs3 Bi2 I9 (CBI) films changes from dark red to transparent. More interestingly, the underlying reason is found to be the interactions between MA0 and Bi3+ with the formation of an amorphous liquefied transparent intermediate phase, which is different from that of lead-based perovskite systems. Moreover, the generality of this approach is demonstrated with other amine gases, including ethylamine (C2 H5 NH2 , EA0 ) and butylamine (CH3 (CH2 )3 NH2 , BA0 ), and another compound, Cs3 Sb2 I9 , by observing a similar reversible optical bleaching phenomenon. The potential for the application of CABB and CBI films in switchable smart windows is investigated. This study provides valuable insights into the interactions between amine gases and lead-free perovskites, opening up new possibilities for high-efficiency optoelectronic and stimuli-responsive applications of these emerging Bi-based materials.

Improved Performance of Organic Thermoelectric Generators Through Interfacial Energetics

The interfacial energetics are known to play a crucial role in organic diodes, transistors, and sensors. Designing the metal-organic interface has been a tool to optimize the performance of organic (opto)electronic devices, but this is not reported for organic thermoelectrics. In this work, it is demonstrated that the electrical power of organic thermoelectric generators (OTEGs) is also strongly dependent on the metal-organic interfacial energetics. Without changing the thermoelectric figure of merit (ZT) of polythiophene-based conducting polymers, the generated power of an OTEG can vary by three orders of magnitude simply by tuning the work function of the metal contact to reach above 1000 µW cm^-2 . The effective Seebeck coefficient (S_eff ) of a metal/polymer/metal single leg OTEG includes an interfacial contribution (V_inter /ΔT) in addition to the intrinsic bulk Seebeck coefficient of the polythiophenes, such that S_eff  = S + V_inter /ΔT varies from 22.7 µV K^-1 [9.4 µV K^-1 ] with Al to 50.5 µV K^-1 [26.3 µV K^-1 ] with Pt for poly(3,4-ethylenedioxythiophene):p-toluenesulfonate [poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)]. Spectroscopic techniques are used to reveal a redox interfacial reaction affecting locally the doping level of the polymer at the vicinity of the metal-organic interface and conclude that the energetics at the metal-polymer interface provides a new strategy to enhance the performance of OTEGs.

The exchange of the fast substrate water in the S2 state of photosystem II is limited by diffusion of bulk water through channels - implications for the water oxidation mechanism

The molecular oxygen we breathe is produced from water-derived oxygen species bound to the Mn4CaO5 cluster in photosystem II (PSII). Present research points to the central oxo-bridge O5 as the 'slow exchanging substrate water (Ws)', while, in the S2 state, the terminal water ligands W2 and W3 are both discussed as the 'fast exchanging substrate water (Wf)'. A critical point for the assignment of Wf is whether or not its exchange with bulk water is limited by barriers in the channels leading to the Mn4CaO5 cluster. In this study, we measured the rates of H2 16O/H2 18O substrate water exchange in the S2 and S3 states of PSII core complexes from wild-type (WT) Synechocystis sp. PCC 6803, and from two mutants, D1-D61A and D1-E189Q, that are expected to alter water access via the Cl1/O4 channels and the O1 channel, respectively. We found that the exchange rates of Wf and Ws were unaffected by the E189Q mutation (O1 channel), but strongly perturbed by the D61A mutation (Cl1/O4 channel). It is concluded that all channels have restrictions limiting the isotopic equilibration of the inner water pool near the Mn4CaO5 cluster, and that D61 participates in one such barrier. In the D61A mutant this barrier is lowered so that Wf exchange occurs more rapidly. This finding removes the main argument against Ca-bound W3 as fast substrate water in the S2 state, namely the indifference of the rate of Wf exchange towards Ca/Sr substitution.

Characterizing natural degradation of tetrachloroethene (PCE) using a multidisciplinary approach

A site in mid-western Sweden contaminated with chlorinated solvents originating from a previous dry cleaning facility, was investigated using conventional groundwater analysis combined with compound-specific isotope data of carbon, microbial DNA analysis, and geoelectrical tomography techniques. We show the value of this multidisciplinary approach, as the different results supported each interpretation, and show where natural degradation occurs at the site. The zone where natural degradation occurred was identified in the transition between two geological units, where the change in hydraulic conductivity may have facilitated biofilm formation and microbial activity. This observation was confirmed by all methods and the examination of the impact of geological conditions on the biotransformation process was facilitated by the unique combination of the applied methods. There is thus significant benefit from deploying an extended array of methods for these investigations, with the potential to reduce costs involved in remediation of contaminated sediment and groundwater.

Synthesis of Vertically Aligned ZnO Nanorods Using Sol-gel Seeding and Colloidal Lithography Patterning

Different ZnO nanostructures can be grown using low-cost chemical bath deposition. Although this technique is cost-efficient and flexible, the final structures are usually randomly oriented and hardly controllable in terms of homogeneity and surface density. In this work, we use colloidal lithography to pattern (100) silicon substrates to fully control the nanorods' morphology and density. Moreover, a sol-gel prepared ZnO seed layer was employed to compensate for the lattice mismatch between the silicon substrate and ZnO nanorods. The results show a successful growth of vertically aligned ZnO nanorods with controllable diameter and density in the designated openings in the patterned resist mask deposited on the seed layer. Our method can be used to fabricate optimized devices where vertically ordered ZnO nanorods of high crystalline quality are crucial for the device performance.

A method for studying pico to microsecond time-resolved core-level spectroscopy used to investigate electron dynamics in quantum dots

Time-resolved photoelectron spectroscopy can give insights into carrier dynamics and offers the possibility of element and site-specific information through the measurements of core levels. In this paper, we demonstrate that this method can access electrons dynamics in PbS quantum dots over a wide time window spanning from pico- to microseconds in a single experiment carried out at the synchrotron facility BESSY II. The method is sensitive to small changes in core level positions. Fast measurements at low pump fluences are enabled by the use of a pump laser at a lower repetition frequency than the repetition frequency of the X-ray pulses used to probe the core level electrons: Through the use of a time-resolved spectrometer, time-dependent analysis of data from all synchrotron pulses is possible. Furthermore, by picosecond control of the pump laser arrival at the sample relative to the X-ray pulses, a time-resolution limited only by the length of the X-ray pulses is achieved. Using this method, we studied the charge dynamics in thin film samples of PbS quantum dots on n-type MgZnO substrates through time-resolved measurements of the Pb 5d core level. We found a time-resolved core level shift, which we could assign to electron injection and charge accumulation at the MgZnO/PbS quantum dots interface. This assignment was confirmed through the measurement of PbS films with different thicknesses. Our results therefore give insight into the magnitude of the photovoltage generated specifically at the MgZnO/PbS interface and into the timescale of charge transport and electron injection, as well as into the timescale of charge recombination at this interface. It is a unique feature of our method that the timescale of both these processes can be accessed in a single experiment and investigated for a specific interface.

Does co-expression of Yarrowia lipolytica genes encoding Yas1p, Yas2p and Yas3p make a potential alkane-responsive biosensor in Saccharomyces cerevisiae?

Alkane-based biofuels are desirable to produce at a commercial scale as these have properties similar to current petroleum-derived transportation fuels. Rationally engineering microorganisms to produce a desirable compound, such as alkanes, is, however, challenging. Metabolic engineers are therefore increasingly implementing evolutionary engineering approaches combined with high-throughput screening tools, including metabolite biosensors, to identify productive cells. Engineering Saccharomyces cerevisiae to produce alkanes could be facilitated by using an alkane-responsive biosensor, which can potentially be developed from the native alkane-sensing system in Yarrowia lipolytica, a well-known alkane-assimilating yeast. This putative alkane-sensing system is, at least, based on three different transcription factors (TFs) named Yas1p, Yas2p and Yas3p. Although this system is not fully elucidated in Y. lipolytica, we were interested in evaluating the possibility of translating this system into an alkane-responsive biosensor in S. cerevisiae. We evaluated the alkane-sensing system in S. cerevisiae by developing one sensor based on the native Y. lipolytica ALK1 promoter and one sensor based on the native S. cerevisiae CYC1 promoter. In both systems, we found that the TFs Yas1p, Yas2p and Yas3p do not seem to act in the same way as these have been reported to do in their native host. Additional analysis of the TFs suggests that more knowledge regarding their mechanism is needed before a potential alkane-responsive sensor based on the Y. lipolytica system can be established in S. cerevisiae.

The influence of inorganic components and carbon-oxygen surface functionalities in activated hydrothermally carbonized waste materials for water treatment

In this study, we have examined how the activation of hydrothermally carbonized sewage sludge and horse manure influences the inorganic component of these materials and surface chemistry. This was examined through statistical correlations between kinetic tests using trimethoprim, fluconazole, perfluorooctanoic acid, and copper, zinc, and arsenic and physicochemical properties. Yield and inorganic content varied considerably, with potassium hydroxide-activated materials producing lower yields with higher inorganic content. Phosphoric acid activation incorporated inorganically bound phosphorus into the material, although this showed no statistically relevant benefit. A maximum surface area of 1363 m²g^-1 and 343 m²g^-1 was achieved for the horse manure and sewage sludge. Statistical analysis found positive correlations between carbon-oxygen functionalities and trimethoprim, fluconazole, perfluorooctanoic acid, and copper removal, while inorganic content was negatively correlated. Conversely, arsenic removal was positively correlated with inorganic content. This research provides insight into the interactions with the organic/inorganic fraction of activated waste materials for water treatment.

Lignin-Inorganic Interfaces: Chemistry and Applications from Adsorbents to Catalysts and Energy Storage Materials

Lignin is one the most fascinating natural polymers due to its complex aromatic-aliphatic structure. Phenolic hydroxyl and carboxyl groups along with other functional groups provide technical lignins with reactivity and amphiphilic character. Many different lignins have been used as functional agents to facilitate the synthesis and stabilization of inorganic materials. Herein, the use of lignin in the synthesis and chemistry of inorganic materials in selected applications with relevance to sustainable energy and environmental fields is reviewed. In essence, the combination of lignin and inorganic materials creates an interface between soft and hard materials. In many cases it is either this interface or the external lignin surface that provides functionality to the hybrid and composite materials. This Minireview closes with an overview on future directions for this research field that bridges inorganic and lignin materials for a more sustainable future.

Influence of water matrix and hydrochar properties on removal of organic and inorganic contaminants

The removal of contaminants from water using low-cost adsorbents has been widely studied, yet studies employing a realistic water matrix are still lacking. This study investigated the removal of organic compounds (trimethoprim, fluconazole, and perfluorooctanoic acid (PFOA)) and metals (As, Zn, and Cu) from landfill leachate. Additionally, tests in pure water, humic acid, and ion matrices were carried out to better understand how the water matrix affects adsorption. The hydrochars were produced from four feedstocks at three carbonization temperatures. The results show that the removal efficiencies for organic pollutants were low and metal removal by hydrochars was comparable with commercial activated carbon. The removal of all compounds from pure water was substantially lower. Tests with humic acid and ion-containing matrices could not fully explain the increased removal in the landfill leachate, which may be due to the combination of the water matrix and presence of soluble species from the hydrochars.

The impact of hydrothermal carbonization on the surface functionalities of wet waste materials for water treatment applications

Hydrothermal carbonization (HTC) is an energy-efficient thermochemical process for converting wet waste products into value added materials for water treatment. Understanding how HTC influences the physicochemical properties of the resultant materials is critical in optimizing the process for water treatment, where surface functionality and surface area play a major role. In this study, we have examined the HTC of four wet waste streams, sewage sludge, biosludge, fiber sludge, and horse manure at three different temperatures (180 °C, 220 °C, and 260 °C). The physicochemical properties of these materials were examined via FTIR, SEM and BET with their adsorption capacity were assessed using methylene blue. The yield of solid material after hydrothermal carbonization (hydrochar) decreased with increasing temperature for all samples, with the largest impact on horse manure and fiber sludge. These materials also lost the highest degree of oxygen, while HTC had minimal impact on biosludge and sewage sludge. The differences here were due to the varying compositions of each waste material, FTIR identified resonances related to cellulose in horse manure and fiber sludge, which were not detected in biosludge and sewage sludge. Adsorption capacities varied between 9.0 and 68 mg g^-1 with biosludge HTC at 220 °C adsorbing the highest amount. Adsorption also dropped drastically at the highest temperature (260 °C), indicating a correlation between adsorption capacity and HTC conditions. This was attributed to the loss of oxygen functional groups, which can contribute to adsorption. These results suggest that adsorption properties can be tailored both by selection of HTC temperature and feedstock.

C/N ratio and carbon source-dependent lipid production profiling in Rhodotorula toruloides

Microbial oils are lipids produced by oleaginous microorganisms, which can be used as a potential feedstock for oleochemical production. The oleaginous yeast Rhodotorula toruloides can co-produce microbial oils and high-value compounds from low-cost substrates, such as xylose and acetic acid (from hemicellulosic hydrolysates) and raw glycerol (a byproduct of biodiesel production). One step towards economic viability is identifying the best conditions for lipid production, primarily the most suitable carbon-to-nitrogen ratio (C/N). Here, we aimed to identify the best conditions and cultivation mode for lipid production by R. toruloides using various low-cost substrates and a range of C/N ratios (60, 80, 100, and 120). Turbidostat mode was used to achieve a steady state at the maximal specific growth rate and to avoid continuously changing environmental conditions (i.e., C/N ratio) that inherently occur in batch mode. Regardless of the carbon source, higher C/N ratios increased lipid yields (up to 60% on xylose at a C/N of 120) but decreased the specific growth rate. Growth on glycerol resulted in the highest specific growth and lipid production (0.085 g lipids/gDW*h) rates at C/Ns between 60 and 100. We went on to study lipid production using glycerol in both batch and fed-batch modes, which resulted in lower specific lipid production rates compared with turbisdostat, however, fed batch is superior in terms of biomass production and lipid titers. By combining the data we obtained in these experiments with a genome-scale metabolic model of R. toruloides, we identified targets for improvements in lipid production that could be carried out either by metabolic engineering or process optimization.

Synthesis and characterization of single-phase epitaxial Cr2N thin films by reactive magnetron sputtering

Cr₂N is commonly found as a minority phase or inclusion in stainless steel, CrN-based hard coatings, etc. However, studies on phase-pure material for characterization of fundamental properties are limited. Here, Cr₂N thin films were deposited by reactive magnetron sputtering onto (0001) sapphire substrates. X-ray diffraction and pole figure texture analysis show Cr₂N (0001) epitaxial growth. Scanning electron microscopy imaging shows a smooth surface, while transmission electron microscopy and X-ray reflectivity show a uniform and dense film with a density of 6.6 g cm^-3, which is comparable to theoretical bulk values. Annealing the films in air at 400 °C for 96 h shows little signs of oxidation. Nano-indentation shows an elastic-plastic behavior with H = 18.9 GPa and E _r = 265 GPa. The moderate thermal conductivity is 12 W m^-1 K^-1, and the electrical resistivity is 70 μΩ cm. This combination of properties means that Cr₂N may be of interest in applications such as protective coatings, diffusion barriers, capping layers and contact materials.

Refining particle positions using circular symmetry

Particle and object tracking is gaining attention in industrial applications and is commonly applied in: colloidal, biophysical, ecological, and micro-fluidic research. Reliable tracking information is heavily dependent on the system under study and algorithms that correctly determine particle position between images. However, in a real environmental context with the presence of noise including particular or dissolved matter in water, and low and fluctuating light conditions, many algorithms fail to obtain reliable information. We propose a new algorithm, the Circular Symmetry algorithm (C-Sym), for detecting the position of a circular particle with high accuracy and precision in noisy conditions. The algorithm takes advantage of the spatial symmetry of the particle allowing for subpixel accuracy. We compare the proposed algorithm with four different methods using both synthetic and experimental datasets. The results show that C-Sym is the most accurate and precise algorithm when tracking micro-particles in all tested conditions and it has the potential for use in applications including tracking biota in their environment.