Trace NaCl and Na₂EDTA Mediated Synthesis of α‑Calcium Sulfate Hemihydrate in Glycerol–Water Solution

We report a new class of glycerol–water system to transform FGD gypsum into α-calcium sulfate hemihydrate (α-HH) mediated by trace NaCl and Na₂EDTA to regulate the phase transformation rate as well as the crystal morphology to achieve crystals with high mechanical strength. NaCl plays a role in accelerating the nucleation and crystal growth process, whereas Na₂EDTA regulates the morphology of α-HH from columnar to lamellar. The paste made from columnar α-HH with higher aspect ratio deserves higher dry bending/compressive strength of 13.6/37.6 MPa, which is comparable with those prepared in nitrate–water medium, chloride–water medium, or by autoclave method. This study provides an improved alternative of glycerol–water system to transform FGD gypsum into α-HH with controlled morphology, high mechanical strength, and less corrosion to the equipment. We also establish the relationship between the mechanical strength of paste and the aspect ratio of α-HH crystals

Nonlattice Cation-SO₄^2– Ion Pairs in Calcium Sulfate Hemihydrate Nucleation

A novel “[MSO₄]^{(2–<i>b</i>)–} ion pair”-directed mechanism is presented to describe the role of nonlattice cations (M^<i>b</i>+) in the nucleation of calcium sulfate hemihydrate (CaSO₄·0.5H₂O, HH) in glycerol aqueous solution. By forming [MSO₄]^{(2–<i>b</i>)–} ion pairs, univalent M⁺ ions (Li⁺, Na⁺, NH₄⁺, and K⁺) and bivalent M²⁺ ions (Cu²⁺, Zn²⁺, Mn²⁺, and Mg²⁺⁾ significantly increased the concentration of lattice ions (Ca²⁺ and SO₄^2–), resulting in a higher supersaturation of HH and shortening the induction time of HH nucleation. Meanwhile, [MSO₄]^{(2–<i>b</i>)–} ion pairs replaced free SO₄^2– as dominant reactants for HH nucleation. They carried SO₄^2– and decoupled them at the nucleation sites for nucleus formation. The efficiency of M^<i>b</i>+ ions on promoting HH nucleation is governed by its pairing and decoupling capability with SO₄^2–. The difference between M^<i>b</i>+ ion and SO₄^2– in limiting diffusion coefficient (Δ<i>D</i>_M^<i>b</i>+⁰) could characterize these two capabilities and was a robust indicator of the efficiency of M^<i>b</i>+ ion. This work provides a new understanding of cation-assisted crystallization and helps identify regulators for nucleation control

Free Nitrous Acid (FNA)-Based Pretreatment Enhances Methane Production from Waste Activated Sludge

Anaerobic digestion of waste activated sludge (WAS) is currently enjoying renewed interest due to the potential for methane production. However, methane production is often limited by the slow hydrolysis rate and/or poor methane potential of WAS. This study presents a novel pretreatment strategy based on free nitrous acid (FNA or HNO₂) to enhance methane production from WAS. Pretreatment of WAS for 24 h at FNA concentrations up to 2.13 mg N/L substantially enhanced WAS solubilization, with the highest solubilization (0.16 mg chemical oxygen demand (COD)/mg volatile solids (VS), at 2.13 mg HNO₂–N/L) being six times that without FNA pretreatment (0.025 mg COD/mg VS, at 0 mg HNO₂–N/L). Biochemical methane potential tests demonstrated methane production increased with increased FNA concentration used in the pretreatment step. Model-based analysis indicated FNA pretreatment improved both hydrolysis rate and methane potential, with the highest improvement being approximately 50% (from 0.16 to 0.25 d^–1) and 27% (from 201 to 255 L CH₄/kg VS added), respectively, achieved at 1.78–2.13 mg HNO₂–N/L. Further analysis indicated that increased hydrolysis rate and methane potential were related to an increase in rapidly biodegradable substrates, which increased with increased FNA dose, while the slowly biodegradable substrates remained relatively static

Bioconcrete based on sulfate-reducing bacteria granules: cultivation, mechanical properties, and self-healing performance

Using waste-activated sludge as a source for non-axenic sulfate-reducing bacterial (SRB) granules, this study developed an innovative bioconcrete with 1% and 2% SRB granules. The mechanical properties (AS 1012.9 and AS 1012.21) and self-healing performance of bioconcrete was systematically examined. The 28-d compressive strength of bioconcrete samples met the design requirement of 50 MPa and the general limit of 13% for average volume of permeable voids (AVPV). Within 3–4 weeks, both 1% and 2% bioconcrete samples precipitated 300–400 µm of calcite in different water media such as glucose, calcium acetate, tap water, and real wastewater. The SEM analysis revealed that SRB granules survived mortar incorporation and precipitated calcium carbonate in the form of calcite which were further confirmed by EDS and XRD analysis. The tap water healed 1% and 2% bioconcrete samples had water permeabilities 64.2% and 69.9% lower than the control, respectively. The mass loss in 5% sulfuric acid was 3.8% and 3.2% less, respectively, for 1% and 2% bioconcrete specimens with surface calcite deposition after 120 d.</p

Immobilizing Water into Crystal Lattice of Calcium Sulfate for its Separation from Water-in-Oil Emulsion

This work report a facile approach to efficiently separate surfactant-stabilized water (droplet diameter of around 2.0 μm) from water-in-oil emulsion via converting liquid water into solid crystal water followed by removal with centrifugation. The liquid–solid conversion is achieved through the solid-to-solid phase transition of calcium sulfate hemihydrate (CaSO₄. 0.5H₂O, HH) to dihydrate (CaSO₄·2H₂O, DH), which could immobilize the water into crystal lattice of DH. For emulsion of 10 mg mL^–1 water, the immobilization-separation process using polycrystalline HH nanoellipsoids could remove 95.87 wt % water at room temperature. The separation efficiency can be further improved to 99.85 wt % by optimizing the HH dosage, temperature, HH size and crystalline structure. Property examination of the recycled oil confirms that our method has neglectable side-effect on oil quality. The byproduct DH was recycled to alpha-HH (a valuable cemetitious material widely used in construction and binding field), which minimizes the risk of secondary pollution and promotes the practicality of our method. With the high separation efficiency, the “green” feature and the recyclability of DH byproduct, the HH-based immobilization-separation approach is highly promising in purifying oil with undesired water contamination

Stability of Illicit Drugs as Biomarkers in Sewers: From Lab to Reality

Systematic sampling and analysis of wastewater samples are increasingly adopted for estimating drug consumption in communities. An understanding of the in-sewer transportation and transformation of illicit drug biomarkers is critical for reducing the uncertainty of this evidence-based estimation method. In this study, biomarkers stability was investigated in lab-scale sewer reactors with typical sewer conditions. Kinetic models using the Bayesian statistics method were developed to simulate biomarkers transformation in reactors. Furthermore, a field-scale study was conducted in a real pressure sewer pipe with the systematical spiking and sampling of biomarkers and flow tracers. In-sewer degradation was observed for some spiked biomarkers over typical hydraulic retention time (i.e., a few hours). Results indicated that sewer biofilms prominently influenced biomarker stability with the retention time in wastewater. The fits between the measured and the simulated biomarkers transformation demonstrated that the lab-based model could be extended to estimate the changes of biomarkers in real sewers. Results also suggested that the variabilities of biotransformation and analytical accuracy are the two major contributors to the overall estimation uncertainty. Built upon many previous lab-scale studies, this study is one critical step forward in realizing wastewater-based epidemiology by extending biomarker stability investigations from laboratory reactors to real sewers

Tuning Nanoparticle Structure and Surface Strain for Catalysis Optimization

Controlling nanoparticle (NP) surface strain, i.e. compression (or stretch) of surface atoms, is an important approach to tune NP surface chemistry and to optimize NP catalysis for chemical reactions. Here we show that surface Pt strain in the core/shell FePt/Pt NPs with Pt in three atomic layers can be rationally tuned via core structural transition from cubic solid solution [denoted as face centered cubic (fcc)] structure to tetragonal intermetallic [denoted as face centered tetragonal (fct)] structure. The high activity observed from the fct-FePt/Pt NPs for oxygen reduction reaction (ORR) is due to the release of the overcompressed Pt strain by the fct-FePt as suggested by quantum mechanics–molecular mechanics (QM–MM) simulations. The Pt strain effect on ORR can be further optimized when Fe in FePt is partially replaced by Cu. As a result, the fct-FeCuPt/Pt NPs become the most efficient catalyst for ORR and are nearly 10 times more active in specific activity than the commercial Pt catalyst. This structure-induced surface strain control opens up a new path to tune and optimize NP catalysis for ORR and many other chemical reactions

Identification of Active Hydrogen Species on Palladium Nanoparticles for an Enhanced Electrocatalytic Hydrodechlorination of 2,4-Dichlorophenol in Water

Clarifying hydrogen evolution and identifying the active hydrogen species are crucial to the understanding of the electrocatalytic hydrodechlorination (EHDC) mechanism. Here, monodisperse palladium nanoparticles (Pd NPs) are used as a model catalyst to demonstrate the potential-dependent evolutions of three hydrogen species, including adsorbed atomic hydrogen (H*_ads), absorbed atomic hydrogen (H*_abs), and molecular hydrogen (H₂) on Pd NPs, and then their effect on EHDC of 2,4-dichlorophenol (2,4-DCP). Our results show that H*_ads, H*_abs, and H₂ all emerge at −0.65 V (vs Ag/AgCl) and have increased amounts at more negative potentials, except for H*_ads that exhibits a reversed trend with the potential varying from −0.85 to −0.95 V. Overall, the concentrations of these three species evolve in an order of H*_abs < H*_ads < H₂ in the potential range of −0.65 to −0.85 V, H*_ads < H*_abs < H₂ in −0.85 to −1.00 V, and H*_ads < H₂ < H*_abs in −1.00 to −1.10 V. By correlating the evolution of each hydrogen species with 2,4-DCP EHDC kinetics and efficiency, we find that H*_ads is the active species, H*_abs is inert, while H₂ bubbles are detrimental to the EHDC reaction. Accordingly, for an efficient EHDC reaction, a moderate potential is desired to yield sufficient H*_ads and limit H₂ negative effect. Our work presents a systematic investigation on the reaction mechanism of EHDC on Pd catalysts, which should advance the application of EHDC technology in practical environmental remediation

Core/Shell Face-Centered Tetragonal FePd/Pd Nanoparticles as an Efficient Non-Pt Catalyst for the Oxygen Reduction Reaction

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) <i>via</i> reductive annealing of core/shell Pd/Fe₃O₄ NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at ∼8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO₄ with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Our study offers a general approach to enhance Pd catalysis in acid for ORR

Unraveling the Mechanisms of Visible Light Photocatalytic NO Purification on Earth-Abundant Insulator-Based Core–Shell Heterojunctions

Earth-abundant insulators are seldom exploited as photocatalysts. In this work, we constructed a novel family of insulator-based heterojunctions and demonstrated their promising applications in photocatalytic NO purification, even under visible light irradiation. The heterojunction formed between the insulator SrCO₃ and the photosensitizer BiOI, via a special SrCO₃–BiOI core–shell structure, exhibits an enhanced visible light absorbance between 400–600 nm, and an unprecedentedly high photocatalytic NO removal performance. Further density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) analysis revealed that the covalent interaction between the O 2p orbital of the insulator (SrCO₃, n-type) and the Bi 6p orbital of photosensitizer (BiOI, p-type) can provide an electron transfer channel between SrCO₃ and BiOI, allowing the transfer of the photoexcited electrons from the photosensitizer to the conduction band of insulator (confirmed by charge difference distribution analysis and time-resolved fluorescence spectroscopy). The •O₂^– and •OH radicals are the main reactive species in photocatalytic NO oxidation. A reaction pathway study based on both in situ FT-IR and molecular-level simulation of NO adsorption and transformation indicates that this heterojunction can efficiently transform NO to harmless nitrate products via the NO → NO⁺ and NO₂⁺ → nitrate or nitrite routes. This work provides numerous opportunities to explore earth-abundant insulators as visible-light-driven photocatalysts, and also offers a new mechanistic understanding of the role of gas-phase photocatalysis in controlling air pollution