Search

Abstract Alcoholysis of poly(ethylene terephthalate) (PET) waste to produce monomers, including methanolysis to yield dimethyl terephthalate (DMT) and glycolysis to generate bis-2-hydroxyethyl terephthalate (BHET), is a promising strategy in PET waste management. Here, we introduce an efficient PET-alcoholysis approach utilizing an oxygen-vacancy (V o)-rich catalyst under air, achieving space time yield (STY) of 505.2 gDMT·gcat −1·h−1 and 957.1 gBHET·gcat −1·h−1, these results represent 51-fold and 28-fold performance enhancements compared to reactions conducted under N2. In situ spectroscopy, in combination with density functional theory calculations, elucidates the reaction pathways of PET depolymerization. The process involves O2-assisted activation of CH3OH to form CH3OH* and OOH* species at V o-Zn2+–O–Fe3+ sites, highlighting the critical role of V o-Zn2+–O–Fe3+ sites in ester bond activation and C–O bond cleavage. Moreover, a life cycle assessment demonstrates the viability of our approach in closed-loop recycling, achieving 56.0% energy savings and 44.5% reduction in greenhouse-gas emissions. Notably, utilizing PET textile scrap further leads to 58.4% reduction in initial total operating costs. This research offers a sustainable solution to the challenge of PET waste accumulation.

Abstract Soil dissolved organic matter (DOM) is crucial to atmospheric, terrestrial and aquatic environments as well as human life. Here, by characterizing DOM from 89 grassland soils throughout China, we reveal the spatial association between DOM geochemistry in the dry season vs annual ecosystem exchange and cancer cases. The humic-like and high molecular weight (3.4–25 kDa) fractions with lower biodegradability, decline from the northern to the southern regions of China, and are correlated with lower soil respiration and net ecosystem productivity at the continental scale. The

Understanding salt and water transport mechanisms in reverse osmosis (RO) under high pressures and salinities is critical to advancing RO-based brine management technologies. In this study, we investigate the dependence of salt permeance and partitioning on feed salinity and applied pressure. Salt partitioning coefficients were determined using a novel high-pressure quartz crystal microbalance (QCM), and salt permeances were collected using a lab-scale high-pressure dead-end cell. Our results show that salt permeance decreases with respect to feed concentration, in contrast to conventional theories for charged RO membranes. We further show salt partitioning coefficients do not change with applied hydrostatic pressure but are dependent on feed salt concentration. We use non-equilibrium molecular dynamics simulations to show that these trends are explained by salinity and pressure-induced changes to the structure of the polyamide layer, namely osmotic deswelling and compaction. Changes in the polyamide layer thickness and pore size alter the frictional interactions of ions, affecting membrane performance at larger salinities and pressures. These results provide new insights on how structure-performance relationships affect salt transport at higher pressures.

Abstract Ceramic membranes are a promising alternative to polymeric membranes for selective separations, given their ability to operate under harsh chemical conditions. However, current fabrication technologies fail to construct ceramic membranes suitable for selective molecular separations. Herein, we demonstrate a molecular-level design of ceramic thin-film composite membranes with tunable subnanometer pores for precise molecular sieving. Through burning off the distributed carbonaceous species of varied dimensions within hybrid aluminum oxide films, we created membranes with tunable molecular sieving. Specifically, the membranes created with methanol showed exceptional selectivity toward monovalent and divalent salts. We attribute this observed selectivity to the dehydration of the large divalent ions within the subnanometer pores. As a comparison, smaller monovalent ions can rapidly permeate with an intact hydration shell. Lastly, the flux of neutral solutes through each fabricated aluminum oxide membrane was measured for the demonstration of tunable separation capability. Overall, our work provides the scientific basis for the design of ceramic membranes with subnanometer pores for molecular sieving using atomic layer deposition.

Abstract Polymer membranes have been used extensively for Angstrom-scale separation of solutes and molecules. However, the pore size of most polymer membranes has been considered an intrinsic membrane property that cannot be adjusted in operation by applied stimuli. In this work, we show that the pore size of an electrically conductive polyamide membrane can be modulated by an applied voltage in the presence of electrolyte via a mechanism called electrically induced osmotic swelling. Under applied voltage, the highly charged polyamide layer concentrates counter ions in the polymer network via Donnan equilibrium and creates a sizeable osmotic pressure to enlarge the free volume and the effective pore size. The relation between membrane potential and pore size can be quantitatively described using the extended Flory-Rehner theory with Donnan equilibrium. The ability to regulate pore size via applied voltage enables operando modulation of precise molecular separation in-situ. This study demonstrates the amazing capability of electro-regulation of membrane pore size at the Angstrom scale and unveils an important but previously overlooked mechanism of membrane-water-solute interactions.

Abstract Achieving controllable fine-tuning of defects in catalysts at the atomic level has become a zealous pursuit in catalysis-related fields. However, the generation of defects is quite random, and their flexible manipulation lacks theoretical basis. Herein, we present a facile and highly controllable thermal tuning strategy that enables fine control of nanodefects via subtle manipulation of atomic/lattice arrangements in electrocatalysts. Such thermal tuning endows common carbon materials with record high efficiency in electrocatalytic degradation of pollutants. Systematic characterization and calculations demonstrate that an optimal thermal tuning can bring about enhanced electrocatalytic efficiency by manipulating the N-centered annulation–volatilization reactions and C-based sp 3/sp 2 configuration alteration. Benefiting from this tuning strategy, the optimized electrocatalytic anodic membrane successfully achieves >99% pollutant (propranolol) degradation during a flow-through (~2.5 s for contact time), high-flux (424.5 L m−2 h−1), and long-term (>720 min) electrocatalytic filtration test at a very low energy consumption (0.029 ± 0.010 kWh m−3 order−1). Our findings highlight a controllable preparation approach of catalysts while also elucidating the molecular level mechanisms involved.

The surface of polyamide reverse osmosis (RO) membranes which regulates interface-dominated phenomena, such as partitioning and fouling, is the one facing the feed during operation. However, the opposite surface of the polyamide selective layer, the one facing the permeate and in contact with the polysulfone porous support, is commonly analyzed in quartz crystal microbalance (QCM) measurements due to limitations of state-of-the-art transfer methodologies. Such measurements on the back surface cannot be generalized because the polyamide layer is chemically and morphologically asymmetric. Herein, we introduce a simple method to coat QCM sensors with polyamide active layers in the correct orientation (i.e., exposing their front surface) and show that interface-dominated phenomena differ significantly between orientations. We start by describing a transfer protocol to coat any surface with a polyamide layer on its front surface orientation. We then systematically analyze the chemical and morphological differences between the two surfaces of the polyamide layer of a commercial RO membrane. Finally, we demonstrate that interface-dominated phenomena depend on the orientation by showing that NaCl partitioning at pH 6 was 1.3 to 2.3-fold higher on the front surface and that organic fouling with humic acid occurred at a lower rate on this surface. The new method presented herein enables measurements on the front surface of polyamide RO membranes, which should be the standard in any future QCM studies.

Microporous organic nanotubes (MONs) hold considerable promise for designing molecular-sieving membranes because of high microporosity, customizable chemical functionalities, and favorable polymer affinity. Here, the authors report the usage of MONs derived from covalent organic frameworks to engineer 15-nm-thick microporous membranes via interfacial polymerization.

Abstract The lack of electron donors in oxygen-rich aquatic environments limits the ability of natural denitrification to remove excess nitrate, leading to eutrophication of aquatic ecosystems. Herein, we demonstrate that electron-rich substances in river or lake sediments could participate in long-distance electron rebalancing to reduce nitrate in the overlying water. A microstructure containing Dechloromonas and consisting of an inner layer of green rust and an outer layer of lepidocrocite forms in the sediment-water system through synergetic evolution and self-assembly. The microstructure enables long-distance electron transfer from the sediment to dilute nitrate in the overlying water. Specifically, the inner green rust adsorbs nitrate and reduces the kinetic barrier for denitrification via an Fe(II)/Fe(III) redox mediator. Our study reveals the mechanism of spontaneous electron transfer between distant and dilute electron donors and acceptors to achieve denitrification in electron-deficient aquatic systems.

Scale formation may have detrimental effects on the properties and functions of materials’ surfaces. Here the authors report the high scaling resistance of hexagonal boron nitride and relate it to the atomic level structure and interaction with water molecules.

Removal of organic micropollutants from water through advanced oxidation processes is hampered by the excessive input of energy and/or chemicals as well as the large amounts of residuals resulting from incomplete mineralization. Here the authors present a new alternative water purification technology to adsorption and advanced oxidation.

The development of novel materials with ion-selective nanochannels has introduced a new technology for harvesting salinity gradient (blue) energy, namely nanopore power generators (NPGs). In this study, we perform a comprehensive analysis of the practical performance of NPG in both coupon-size and module-scale operations. We show that although NPG membrane coupons can theoretically generate ultrahigh power density under ideal conditions, the resulting power density in practical operations at a coupon scale can hardly reach 10 W·m−2 due to concentration polarization effects. For module-scale NPG operation, we estimate both the power density and specific extractable energy (i.e., extractable energy normalized by the total volume of the working solutions), and elucidate the impact of operating conditions on these two metrics based on the interplay between concentration polarization and extent of mixing of the high- and low-concentration solutions. Further, we develop a modeling framework to assess the viability of an NPG system. Our results demonstrate that, for NPG systems working with seawater and river water, the gross specific extractable energy by the NPG system is very low (~0.1 kW·h·m−3) and is further compromised by the parasitic energy consumptions in the system (notably, pumping of the seawater and river water solutions and their pretreatment). Overall, NPG systems produce very low net specific extractable energy (< 0.025 kW·h·m−3) and net power density (< 0.1 W·m−2). Our study highlights the significant practical limitations in NPG operations, casting doubt on the viability of NPG as a technology for blue energy harvesting.

Electrocatalytic processes are promising for automated and scalable synthesis of singlet oxygen, but they are energy- and chemical-intensive. Here the authors present a Janus electrocatalytic membrane that selectively produces singlet oxygen with low energy consumption and free of chemical precursors.

Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Here, the authors demonstrate that precise solute-solute separation can be achieved using polyamide membranes formed via surfactant-assembly regulated interfacial polymerization.

Increasing the selectivity of desalination membranes is of crucial importance for advancing membrane desalination technologies. Here the authors demonstrate a plasticizing-extracting process for tuning the permselectivity of polymeric membranes and achieving desired desalination performance.