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Abstract Quaternary Mg 2 Si 0.25 Ge 0.05 Sn 0.7 based solid solutions were synthesized by B 2 O 3 flux method combined with spark plasma sintering (SPS) technique. The carrier concentration was tuned by adjustment of the SPS temperature. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured in the temperature range from 320 to 820 K. The results show that the density, carrier concentration and lattice thermal conductivity monotonically increase with sintering temperature. With increasing carrier concentration the electron effective mass increases due to band convergence, while the electron mobility drops dramatically from 70.5 cm2 V−1 s−1 to 7.5 cm2 V−1 s−1. The phonon scattering mechanism in the quaternary solid solutions was analyzed using the Abeles model. The calculation shows that mass fluctuation scattering plays a crucial role in reducing the lattice thermal conductivity. Owing to band convergence combined with scattering of the phonons by point defects, a ZT max of 1.1 at 700 K was obtained for Mg 2 (Si 0.2 Ge 0.1 Sn 0.7) 0.99 Sb 0.01. Graphical abstract Band convergence combined with point defect scattering of phonons leads to a high ZT of 1.1 at 700 K in Mg 2 (Si 0.2 Ge 0.1 Sn 0.7) 0.99 Sb 0.01. fx1 Highlights • Mg 2 (Si,Ge,Sn) solid solutions have been successfully prepared by B 2 O 3 flux method. • Band convergence markedly enhances the Seebeck coefficient. • Mass fluctuation scattering effectively reduces the lattice thermal conductivity. • A ZT max of 1.1 at 700 K was obtained for Mg 2 (Si 0.2 Ge 0.1 Sn 0.7) 0.99 Sb 0.01. [ABSTRACT FROM AUTHOR]

As a potential thermoelectric (TE) material, the high lattice thermal conductivity and relatively low weighted mobility severely limit TE property optimization of InSb binary compound. In this paper, we substituted In of InSb with Ga and systematically investigated the effect of Ga alloying on the Seebeck coefficient, electrical conductivity and lattice thermal conductivity of InSb between 300 K and 770 K. We found that Ga alloying simultaneously reduced the lattice thermal conductivity and optimized the weighted mobility of InSb. The lattice thermal conductivity has been analyzed using Abeles model to gain more insight on the roles of Ga in In 1- x Ga x Sb( x  = 0, 0.1, 0.15, 0.2) solid solution. The synergetic effect of Ga alloying on the electron and phonon transport leads to a marked enhancement in TE potential of InSb. The dimensionless figures of merit of InSb and In 0.8 Ga 0.2 Sb reach, respectively, 0.54 and 0.52 at 770 K. [ABSTRACT FROM AUTHOR]

• Electrodialysis pretreatment showed high recovery efficiency for sludge-derived DOM. • Molecular number in DOM identified with dual ESI modes was increased by 200%. • DOM WAS mainly contained proteins/aliphatic and lipid-like compounds. • DOM ADS was composed of lipids, proteins/aliphatic, and lignins/CRAM-like compounds. • Two ESI analysis modes can recognize different emerging contaminants. High-resolution mass spectrometry was extensively applied in molecular composition and transformation pathways of dissolved organic matter (DOM) in wastewater sludge treatments. Sample pretreatment methods and electrospray ionization (ESI) modes significant affect the accuracy of molecular characterization for DOM. This study investigated the effects of pretreatment methods (styrene divinyl benzene polymer (PPL), octadecyl (C18), and electrodialysis (ED)) on molecular characteristics of DOM in two typical wastewater sludges (waste activated sludge (WAS) and anaerobic digestion sludge (ADS)) analyzed by FT-ICR MS in both positive ESI (ESI (+)) and negative ESI (ESI (−)) modes. The results indicated that ED pretreatment exhibited the highest recovery rate of 70% ‒ 95% for sludge-derived DOM. ED and PPL performed well in recovering the different sludge-derived DOM with a high similarity of molecular characteristics (e.g., lipids, proteins/aliphatic, and lignins/CRAM-like), and the C18 method was ineffective in extracting carbohydrates, unsaturated hydrocarbons, and amino sugars. In addition, compared with single ESI (−) analysis mode, the molecular number identified by ESI (+) analysis mode was increased by 200%, especially, more unsaturated hydrocarbons and N-containing compounds were detected. Except for biogenic DOM, plenty of emerging containments (ECs) in sludge-derived DOM were identified; ESI (−) mode was more effectively in recognizing the alkyl benzene sulfonic acids (e.g., anionic surfactants); and ESI (+) mode was more effectively for plasticizers identification, for example, dioctyl terephthalate and dibutyl phthalate. This study illustrated that ED pretreatment coupled with FT-ICR MS in dual ESI modes could give more insights in complexed molecular information for DOM in wastewater sludge, and provides a theoretical basis for subsequent sludge treatments and disposals. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • AHT at high pH promoted hydrolysis of protein-like and heterocyclic-N compounds. • Harmful aromatics were degraded in AHT at high pH. • Increasing pH in AHT improved plant fertility of ADS-derived DOMs. • Amino compounds and humic substances are key to promote plant growth. Recovering high-value biomaterials from anaerobic digestion sludge (ADS) has attracted considerable attention. However, the molecular features and biological effects of abundant dissolved organic matters (DOMs) in ADS are still unclear, which limits the efficient recycling and application of these bioproducts. This study investigated the molecular composition and transformation of DOMs recovered from ADS through a mild-temperature alkali-hydrothermal treatment (AHT) with ultrahigh-resolution mass spectrometry and energy spectroscopy, and the fertilizing effects of DOMs were evaluated by rice hydroponics. The results indicated that AHT processes significantly promoted the solubilization and release of DOMs from ADS, where most of DOMs molecules remained unchanged and mainly consisted of N-containing compounds with 1–3 N atoms, featuring aromatic or N-heterocyclic rings. Furthermore, AHT processes at pH of 9–10 induced the hydrolysis of partial protein-like substances in DOMs, which was accompanied by formation of heterocyclic-N compounds. Under AHT at pH of 11–12, protein-like and heterocyclic-N substances were increasingly decomposed into amino-N compounds containing 1 or 5 N atoms, while numerous oxygenated aromatic substances with phytotoxicity were degraded and removed from DOMs. Rice hydroponic test verified that ADS-derived DOMs recovered by AHT process at pH of 12 exhibited the highest bioactivity for rice growth, which was attributed to the abundance of amino compounds and humic substances. This study proposed a novel process for the recovery of high-quality liquid organic fertilizer from ADS through AHT process, which can further enrich the technical options available for the safe utilization of sludge resources. [ABSTRACT FROM AUTHOR]

Sludge pyrolysis carbonization has shown potential to convert sludge biomass into multifunctional carbon materials. However, ecological risks of dissolved organic matters (DOMs) with obscure molecular characteristics retaining in sludge-based carbons (SBCs) have received little attention. This study investigated the impact of pyrolysis temperatures on the molecular conversion and biotoxicity effects of DOMs in SBCs. The results revealed that DOMs in SBCs 300–400 were mainly derived from depolymerization of biopolymers and the polycondensation and cyclization of small intermediate molecules, which mainly consisted of aromatic CHON compounds with 1–3 N atoms, featuring high unsaturation and molecular weights. High-temperature pyrolysis (500–800 °C) promoted the decomposition and ring-opening of aromatic CHON compounds into saturated aliphatic CHO compounds with 2–4 O atoms in SBCs 500–800. Noteworthily, SBCs 300–400 -derived DOMs showed relatively strong biotoxicity on the growth and development of wild-type zebrafish embryos, pakchoi seeds, and Vibrio qinghaiensis Q67, which was significantly related to aromatic amines, phenols, and heterocyclic-N compounds in DOMs of SBCs 300–400. SBCs 500–800 -derived DOMs were mainly straight-chain fatty acids and showed no observable acute biotoxicity. This study highlights the negative impact of DOMs in SBCs on the ecological environment, and provides the theoretical basis for controlling toxic byproducts in sludge pyrolysis process. [Display omitted] • DOMs in SBCs 300–400 mainly contained N-containing aromatic compounds. • DOMs of SBCs 500–800 were mainly composed of saturated aliphatic compounds. • Biotoxicity was related to aromatic amines, phenols, and heterocyclic-N compounds. • Increasing pyrolysis temperature can reduce the content and biotoxicity of DOMs in SBCs. [ABSTRACT FROM AUTHOR]

Sludge pyrolysis carbonization has shown potential to convert sludge biomass into multifunctional carbon materials. However, ecological risks of dissolved organic matters (DOMs) with obscure molecular characteristics retaining in sludge-based carbons (SBCs) have received little attention. This study investigated the impact of pyrolysis temperatures on the molecular conversion and biotoxicity effects of DOMs in SBCs. The results revealed that DOMs in SBCs 300–400 were mainly derived from depolymerization of biopolymers and the polycondensation and cyclization of small intermediate molecules, which mainly consisted of aromatic CHON compounds with 1–3 N atoms, featuring high unsaturation and molecular weights. High-temperature pyrolysis (500–800 °C) promoted the decomposition and ring-opening of aromatic CHON compounds into saturated aliphatic CHO compounds with 2–4 O atoms in SBCs 500–800. Noteworthily, SBCs 300–400 -derived DOMs showed relatively strong biotoxicity on the growth and development of wild-type zebrafish embryos, pakchoi seeds, and Vibrio qinghaiensis Q67, which was significantly related to aromatic amines, phenols, and heterocyclic-N compounds in DOMs of SBCs 300–400. SBCs 500–800 -derived DOMs were mainly straight-chain fatty acids and showed no observable acute biotoxicity. This study highlights the negative impact of DOMs in SBCs on the ecological environment, and provides the theoretical basis for controlling toxic byproducts in sludge pyrolysis process. [Display omitted] • DOMs in SBCs 300–400 mainly contained N-containing aromatic compounds. • DOMs of SBCs 500–800 were mainly composed of saturated aliphatic compounds. • Biotoxicity was related to aromatic amines, phenols, and heterocyclic-N compounds. • Increasing pyrolysis temperature can reduce the content and biotoxicity of DOMs in SBCs. [ABSTRACT FROM AUTHOR]

N-type Mg2Si0.59 − xSn0.41Sb x (0 ≤ x ≤ 0.01) solid solutions were prepared by melting elemental metals in sealed tantalum tubes followed by hot pressing. The electrical conductivity, Seebeck coefficient, and thermal conductivity have been measured as a function of temperature from 300 to 770 K. The electron effective mass and electron concentration increase with increasing Sb doping amount. The Sb doping enhances the concentration of Mg vacancies, which reduces the electron concentration. The maximum dimensionless figure of merit is 0.68 at 693 K for the x = 0.005 sample. [ABSTRACT FROM AUTHOR]

XSb (X = Ga, In) based thermoelectric (TE) materials have received much attention due to the high electronic performance. However, the high lattice thermal conductivity limits further TE performance enhancement. In this work, GaSb 1- x Te x (x ≤ 0.12) compounds were prepared to investigate the effect of Ga vacancies induced by Te doping on the lattice thermal conductivity. The room temperature lattice thermal conductivity decreases significantly from ~24 Wm−1K−1 for GaSb to ~3.4 Wm−1K−1 for GaSb 0.88 Te 0.12. The Callaway model was used to analyze the detailed phonon scattering mechanism. The effect of each scattering mechanism at different phonon frequencies and temperatures are investigated. The lattice thermal conductivity reduction due to vacancies combined with isoelectronic substitution is predicted. These results are of importance for further TE performance enhancement of the XSb (X = Ga, In) based TE materials. • GaSb1- x Te x (x ≤0.12) compounds were successfully prepared by B2O3 flux method. • The lattice thermal conductivity of GaSb was significantly reduced by Ga vacancies. • The strong strain field fluctuation effectively scatters high frequency phonons. • A lowest lattice thermal conductivity of 1.5 Wm-1K-1 was predicted. [ABSTRACT FROM AUTHOR]

Abstract: N-type Mg2Si0.58Sn0.42− x Bi x (0≤ x ≤0.015) compounds were prepared by melting the element metals in sealed tantalum tubes followed by hot pressing. The XRD results indicate that all samples are composites containing both major magnesium silicide solution phase and minor magnesium stannide solution phase. The Hall measurements show that the carrier concentrations and electrical conductivities increase with the increase of Bi doping amount. It was found that the intrinsic excitation shifts to high temperature due to Bi doping, which leads to the increase of the peak-temperatures of the Seebeck coefficient. The maximum dimensionless figure of merit is 0.65 at 700K for the sample x =0.015. [Copyright &y& Elsevier]

The high carrier mobility and narrow band gap underpin the thermoelectric promise of InSb. However, the simple crystal structure, susceptibility of carrier mobility to crystallographic defects, and intrinsically high lattice thermal conductivity are hindrances. Here, we reported an approach that combines isoelectronic substitution and vacancies. First, we iso-electronically substituted In with Ga. We found that more Ga than previously thought could be doped in InSb at the expense of forming secondary phase. The analysis by the Abeles model indicated that strain field fluctuations are the dominant mechanism in phonon scattering. A ZT max of 0.57 at 780 K was obtained in the sample of In 0.6 Ga 0.4 Sb. Next, we implemented cationic vacancies via Te doping to regulate the carrier concentration and carrier mobility. We found the Te doping suppresses the phase separation. The analysis of Callaway model helped identify the specific contribution of various phonon scattering mechanisms. A ZT max of 0.4 at 780 K was obtained in the sample of In 0.85 Ga 0.15 Sb. Finally, we introduced anionic vacancies via excess In. We found that the anion vacancies increased the carrier concentration and suppressed the bipolar effect. A ZT max of 0.59 at 780 K was obtained in In 0.87 Ga 0.15 Sb. The Ga substitution combined with vacancies led to a significant reduction of lattice thermal conductivity of InSb over a wide temperature range. The analysis by the Callaway model showed strain field fluctuations play a crucial role in scattering phonons. Image 1 • (In,Ga)Sb solid solutions were prepared by B 2 O 3 flux method. • Cationic vacancies significantly reduce the lattice thermal conductivity. • Strain field fluctuation was markedly enhanced by cationic vacancies. • Anionic vacancies effectively depress the bipolar effect. • A ZT max of 0.59 at 780 K was obtained in In 0.87 Ga 0.15 Sb. [ABSTRACT FROM AUTHOR]

In this work we have observed the beneficial effect from the solid solution formation on the thermoelectric performance of (Cu 2(1 − x ) Sb 2 x Te)(Ga 2 Te 3 ) 3 upon Sb substitution for Cu. This substitution allows the different occupations of Sb in the crystal lattice, i.e. Sb at Cu sites with x ≤ 0.05 and at Ga sides with x ≥ 0.05, which has resulted in the Pisarenko relation does not exactly capture the measured Seebeck coefficient under assumed effective masses m *. The reduction of the lattice thermal conductivity ( κ L ) has been quantified within the temperature range from room temperature to 723 K. Over the entire composition range, the κ L value is reduced by 33% and 25% at temperature 723 K and 580 K, respectively. This observation is in a good agreement with the theoretical calculation based on the Callaway model used in the solid solutions. Along with the increasing of the mobility and electrical conductivity, the thermoelectric performance has been improved with the highest ZT value of 0.58 at 723 K, which is about double the value of intrinsic (Cu 2 Te)(Ga 2 Te 3 ) 3 . [ABSTRACT FROM AUTHOR]

In this work we have observed a remarkable improvement in the thermoelectric (TE) performance of In6- xSn xSe7 ( ZT = ∼0.28 at x = 0.1, 833 K) compared to that of pristine In6Se7 ( ZT = 0.015 at 640 K). This improvement is mainly attributed to the creation of active donor defects SnIn3+ as Sn(4+) is energetically favorable to In+ sites. Although Sn (2+), which generates a defect SnIn− as an acceptor when it is incorporated into the In3+ sites, has a negative effect on the transport properties, the counter effect from Sn(4+) and Sn(2+) suggests that In6Se7-based alloys are prospectively good thermoelectric candidates if their chemical compositions are well optimized. [ABSTRACT FROM AUTHOR]

In this work, we have observed the enhancement of carrier concentration in α-In2Se3 at a specific S content. This enhancement results from avoiding the annihilation of defects, such as VIn and interstitial Ini acting as donors, via the rearrangement of both the cationic and anionic disorders. Therefore, there is a remarkable improvement in electrical conductivity ( σ). For example, the sample α-In2S0.05Se2.95 perpendicular to the pressing direction ( C┴) gives the highest σ value of 5.56 × 103 Ω−1 m−1 at 923 K, while the virgin α-In2Se3 gives only 9.17 × 102 Ω−1 m−1. In addition, there are dual effects on the lattice thermal conductivity ( κL) resulting from the stabilization of the lattice structure caused by the rearrangement of defect disorder and the lattice distortion from the formation of defect SSe. Therefore, the lattice contribution ( κL) in S-incorporated α-In2Se3 remains relatively high at high temperatures. As a consequence, we have improved the thermoelectric performance, achieving a ZT value of 0.67 for α-In2S0.05Se2.95 at 923 K, which is about 2.8 times that of virgin α-In2Se3 ( ZT = 0.24 at C┴). [ABSTRACT FROM AUTHOR]

In Ga 2 Te 3 -rich quasibinary Cd (3 − 3 m ) Ga 2 m Te 3 ( m = 0.75–0.98) system there are two physical phenomena: structural vacancy ( V ) and its related cationic interdiffusion. The former is able to simultaneously govern the carrier, phonon transportations and the bandgap, while the latter merely facilitates the transportation of carrier to some extent. Accordingly, there are multiple transportation behaviors coexisting at a certain m value in this system. These behaviors, which have not only enhanced the carrier concentration ( n ), but have also increased the entropy of the lattice as m value increases, yield the highest thermoelectric figure of merit ( ZT ) of 0.55 at 682 K for m = 0.98. [ABSTRACT FROM AUTHOR]

In this study, the molecular transformation of sludge biopolymers during hydrothermal treatment with the temperature ranging from 25 °C to 200 °C was examined and was seen to significantly affect the macrophysical properties (dewaterability and rheological property) of sludge. The results showed that the sludge dewaterability and flow ability under high shear stress deteriorated by a hydrothermal process at 25 °C to 120 °C, but the deterioration alleviated above the temperature threshold of 120 °C. The consistence of changes in sludge dewaterability and rheological property in HT process was mainly attributed to the variation in gel properties of soluble biopolymer. Two-stage changes in biopolymer transformation were identified, beginning with a solubilization stage from 25 °C to 120 °C in which a biopolymer with a gel-like network structure was released into liquid phase, creating flow resistance under high shear stress such that sludge dewaterability deteriorated. The second stage was identified as a conversion stage (120 °C–200 °C) in which proteins and polysaccharides hydrolyzed and experienced a Maillard reaction, leading to the degradation of the biopolymer network structure. The newly formed recalcitrant Maillard products showed weak flow response to high shear stress, allowing for an improvement in sludge dewaterability. The pathways of a Maillard reaction were identified via gas chromatography−mass spectrometer (GC–MS), 1H nuclear magnetic resonance spectroscopy (1H NMR) and two-dimensional correlation spectral analysis (2D-COS) of Fourier-transform infrared spectrometer (FTIR), etc. Three-dimensional excitation-emission matrix (3D-EEM) proved to be an applicable method for tracking Maillard reaction in sludge hydrothermal process due to the distinctive fluorescence characteristics of Maillard products. This study further clarifies the obscure process of sludge hydrothermal treatment and will help improve the accuracy of subsequent research. Unlabelled Image • Biopolymers release enhanced sludge gel-like property in low-temperature of HT process. • Maillard reaction degree was related to sludge dewaterability at higher HT temperature. • Fluorescence peak (λ ex/em = 350 nm/430 nm) was related to Maillard products. • Pathways of Maillard reaction was proposed based on spectroscopic evidences. • The relationships of biopolymers evolution and physical properties were established. [ABSTRACT FROM AUTHOR]

Abstract It is challenging to fabricate a starch derivative with a plasticizing effect and good dispersion in a poly(lactic acid) matrix to achieve desirable performance. In this study, self-suspended starch fluids composed of modified granules as the core and polyethylene glycol-substituted tertiary amines as the shell were first fabricated via a combined carboxymethylation and acylation reaction. The as-prepared starch fluids exhibited liquid-like behavior and had semiconductor electric conductivity (4.91 × 10−5 S/cm) at room temperature without a solvent. The modulus of starch fluids was clearly reduced under the heating process and exhibited its initial flow properties upon cooling, displaying thermo-reversible behavior. The resultant fluids were then incorporated into a poly(lactic acid) matrix to produce fully biodegradable composites with desirable performance. At a loading level of 10 wt%, starch fluids exhibited simultaneous enhancements in elongation at break (increase of 164.7%) and thermal conductivity (increase of 119%) of PLA composites compared to pure PLA, attributable to the good dispersion and heat-transfer properties of starch fluids. In addition, PLA composites with 10 wt% loading of starch fluids demonstrated excellent antistatic performance (3.08 × 10−4 S/cm), suggesting that polar groups of the PLA structure and PEG groups of starch fluids contributed synergistically to the electrical conductivities of composites. These results indicate that starch fluids are promising antistatic agents and plasticizers for potential applications in biodegradable materials. [ABSTRACT FROM AUTHOR]

Here, we present the manipulation of the crystal structure defects: an alternative route to reduce the lattice thermal conductivity (κL) on an atomic scale and improve the thermoelectric performance of CuGaTe2. This semiconductor with defects, represented by anion position displacement (u) and tetragonal deformation (η), generally gives low κL values when u and η distinctly deviate from 0.25 and 1 in the ideal zinc-blende structure, respectively. However, this semiconductor will show high Seebeck coefficients and low electrical conductivities when u and η are close to 0.25 and 1, respectively, due to the electrical inactivity caused by an attractive interaction between donor-acceptor defect pairs (GaCu2+ + 2VCu-). [ABSTRACT FROM AUTHOR]

Abstract: Mg2X (X = Si, Ge, and Sn) compounds have attracted increasing attention owing to their promising thermoelectric properties and “green” constituent elements. While most studies to date have been on n-type Mg2(Si,Sn) solid solutions, we herein report Ag-doping study in Mg2(Ge,Sn) solid solutions to pursue higher p-type performance. Two series of samples, Mg2Ge1−x Sn x and Mg2−y Ag y Ge0.4Sn0.6, were prepared by melting in evacuated Ta tubes, followed by hot pressing, and the thermoelectric properties of the solid solutions were investigated from room temperature to 723 K. An n- to p-type crossover in the Seebeck coefficient was observed for Mg2Ge0.4Sn0.6 and Mg2Ge0.2Sn0.8 at elevated temperatures. To enhance p-type performance, we doped Ag in Mg2Ge0.4Sn0.6 that exhibited lowest thermal conductivity among the Mg2(Ge,Sn) solid solutions. It was found that (1) p-type behavior has been established in Mg2−y Ag y Ge0.4Sn0.6 (y = 0.005, 0.01, 0.02, 0.04) samples in the entire temperature range studied; and (2) the electrical conductivity increased with increasing Ag content until reaching the solution limit ∼0.02. As a result, a dimensionless figure of merit ZT ∼0.38 is attained for Mg1.98Ge0.4Sn0.6Ag0.02 at 675 K, which is one of the highest reported values in p-type Mg2X compounds. [Copyright &y& Elsevier]

In this work the chalcopyrite CuIn3Se5−xTex (x = 0~0.5) with space group through isoelectronic substitution of Te for Se have been prepared, and the crystal structure dilation has been observed with increasing Te content. This substitution allows the anion position displacement ∆u = 0.25-u to be zero at x ≈ 0.15. However, the material at x = 0.1 (∆u = 0.15 × 10−3), which is the critical Te content, presents the best thermoelectric (TE) performance with dimensionless figure of merit ZT = 0.4 at 930 K. As x value increases from 0.1, the quality factor B, which informs about how large a ZT can be expected for any given material, decreases, and the TE performance degrades gradually due to the reduction in nH and enhancement in κL. Combining with the ZTs from several chalcopyrite compounds, it is believable that the best thermoelectric performance can be achieved at a certain ∆u value (∆u ≠ 0) for a specific space group if their crystal structures can be engineered. [ABSTRACT FROM AUTHOR]