Search

Abstract: The density functional method PW91P86 with relativistic effective core potentials (RECPs) and LANL2DZ basis set has been used to investigate the possible stable geometrical configurations and relative stabilities of the lowest-lying isomers of rhodium-doped gold clusters, Au n Rh (n=1–8). Several low-lying isomers were determined. The results indicate that the ground-state Au n Rh, n=1–8, clusters have planar structures except for n=5 and 8. The stability trend of the Au n Rh clusters shows that the clusters with even numbers of atoms are more stable than the clusters with odd numbers of atoms, indicating that the Au5Rh cluster is a magic cluster with high chemical stability. [Copyright &y& Elsevier]

Abstract: Nickel-doped gold cluster anions, Au n Ni− (n =1–5), were investigated using the density functional method B3LYP with relativistic effective core potentials (RECP) and LANL2DZ basis set. The possible stable geometrical configurations with their electronic states are determined, and many of them in electronic configurations with a high spin multiplicity. The stability trend of the anionic clusters is compared to that of neutral clusters. Our results show that the one excess electron is strong enough to modify the known growth pattern and stability trend of the neutral Au n Ni clusters, and indicate that the stability and electron affinity of the clusters alter with odd-even oscillations as a function of the number of gold atoms. [Copyright &y& Elsevier]

The structural, electronic, and spectral properties of Al n Cu k (n = 1–16; k = 0, ±1) clusters have been examined via ab initio calculations combined with the CALYPSO method. It is found that the Cu atom in the ground-state Al n Cu k cluster is situated on the surface for n = 1–11 and prefers a central site for n = 12–16 (except for in Al 15 Cu, Al 12 Cu+, and Al 16 Cu+). The stability, chemical activity, ionization potential, and electron affinity of the Al n Cu k clusters are closely linked to the cluster size, the number of valence electrons, the point group, and the spin state. Simultaneously, we simulated UV spectra, photoelectron spectra, and vibrational and Raman spectra of the Al n Cu k clusters. The global minimum structure of the A l n Cu− cluster is recognized by our comparing the simulated and measured photoelectron spectra. The spectra and orbital of Al 13 Cu alloy cluster. [Display omitted] • The dopant Cu atom in big aluminum clusters tends to occupy the most highly coordinated location. • The closed-shell structures are able to significantly enhance the stability of the Al n Cuk clusters. • The symmetry of Cu-doped aluminum cluster has a large influence on its chemical activity. • The major dissociation products of Al n Cu + cluster is Al+(or Al) and Al n-1 Cu (or Al n-1 Cu+). [ABSTRACT FROM AUTHOR]

The ground-state structures, electronic properties and spectra of Ti n c ( n = 3–16 and c = 0, ±1) clusters have been investigated based on density functional theory (DFT) and CALYPSO structure prediction. Geometry optimizations show that the neutral, cationic and anionic titanium clusters have the same growth pattern. The pentagonal bipyramid plays an important role in the growth process. Analysis of electronic properties shows that the thermal stability of cationic and anionic clusters is greater than that of neutral cluster. The pentagonal bipyramid and icosahedron clusters have relatively high stability. Chemical activity of titanium clusters decreases with the cluster size. The preferred dissociation pathway of Ti n + clusters is the loss of a single Ti atom to form Ti n − 1 +. Optical absorption of Ti n clusters and infrared and Raman spectra of Ti n + clusters have been simulated and can be used for their structural identification. The ground states of Ti n − clusters have been determined by comparing experimental and theoretical photoelectron spectra. • The pentagonal bipyramid plays an important role in the growth process of titanium clusters • The titanium cluster with pentagonal bipyramid or icosahedron geometry is more table than other clusters. • The preferred dissociation pathway of Ti n + clusters is the loss of a single Ti atom to form Ti n − 1 +. • The ground state of anionic Ti n − clusters are identified by photoelectron spectra.s [ABSTRACT FROM AUTHOR]

Abstract: Ab initio method based on density-functional theory has been used to investigate the Au n Pd− (n=1–5) cluster anions. The possible stable geometrical configurations with their electronic states are determined, and the energy gaps between the HOMO and LUMO of the ground states are investigated. Our results show that the one excess electron is strong enough to modify the known growth pattern of the neutral Au n Pd clusters, and indicate that the larger is the Au n Pd cluster, the smaller are the distortions by the one excess electron. [Copyright &y& Elsevier]

[Display omitted] • Self-acidification was mainly attributed to sulfur disproportionation. • Supplying alkalinity to bulk was essential to control self-acidification. • S0FB achieved 7–129 times higher of TN removal rate than S0PB. • S0FB achieved 26–65 times higher of TP removal rate than S0PB. The sulfur fluidizing bioreactor (S0FB) has significant superiorities in treating nitrate-rich wastewater. However, substantial self-acidification has been observed in engineering applications, resulting in frequent start-up failures. In this study, self-acidification was reproduced in a lab-scale S0FB. It was demonstrated that self-acidification was mainly induced by sulfur disproportionation process, accounting for 93.4 % of proton generation. Supplying sufficient alkalinity to both the influent (3000 mg/L) and the bulk (2000 mg/L) of S0FB was essential for achieving a successful start-up. Furthermore, the S0FB reached 10.3 kg-N/m3/d of nitrogen removal rate and 0.13 kg-PO 4 3-/m3/d of phosphate removal rate, respectively, surpassing those of the documented sulfur packing bioreactors by 7–129 times and 26–65 times. This study offers a feasible and practical method to avoid self-acidification during restart of S0FB and highlights the considerable potential of S0FB in the treatment of nitrate-rich wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • The deficient inorganic N, P, and C sources induced decline in S0AD efficiency. • Specific thresholds for inorganic N, P, and C to robust S0AD were established. • Substantial reduction in SOBs occurred under deficient inorganic nutrients. • External supplying mitigated nutrient constraints in a pilot-scale S0PB bioreactor. Elemental sulfur packed-bed (S0PB) bioreactors are increasingly employed to treat secondary effluents from wastewater treatment plants. Limited availability of inorganic nutrients, such as ammonium, phosphate, and inorganic carbon, significantly determines the growth of autotrophic microorganisms and the denitrification efficiency. This study investigated the constraining thresholds of inorganic nutrients on the elemental sulfur autotrophic denitrification process. In the absence of ammonium, phosphate, and bicarbonate, the denitrification rate decreased. Specifically, the ammonium assimilation process could be replaced by nitrate assimilation pathways, resulting in a 29.5 % decline in denitrification efficiency when the ammonium-N feed was reduced from 2.0 to 0 mg-N/L. However, the absence of phosphate-P and bicarbonate-C led to substantial drops in denitrification efficiency by 66.7 % and 77.5 %, respectively. This was primarily attributed to diminished biomass yield, as evidenced by reductions of 77.8–82.6 % in ATP and 35.7–44.3 % in protein content, along with a 12.4 %–14.7 % decrease in the relative abundances of dominant sulfur-oxidizing bacteria. Correlation analyses established specific thresholds for desired nitrate removal amounts: 0.131 for ammonium-N, 0.053 for phosphate-P, and 0.597 for bicarbonate-C. These thresholds provided valuable guidance for adjusting real-life wastewater through external supplementation when employing a pilot-scale S0PB bioreactor, leading to a significant enhancement of denitrification efficiency. This study emphasizes the significance of considering the concentrations of inorganic nutrients in wastewater when implementing S0PB bioreactors, which is a context that frequently neglects potential negative consequences. [ABSTRACT FROM AUTHOR]

[Display omitted] • SADP process was independently and controllably maintained in sulfur PBR. • SAD2 system achieved 2.38 times higher of SADN rate by the assist of SADP. • SADP-S2− had higher biocompatibility than chemical-S2− (Na 2 S). • Bioaugmentation and polysulfuration by SADP-S2− stimulated S0 utilization rate. • An applicable pattern of SAD2 system was supposed. Sulfur-based autotrophic disproportionation (SADP) has been accidentally discovered during employing sulfur-based autotrophic denitrification (SADN) bioreactor to treat low C/N ratio wastewater. The SADP products, including sulfide (SADP-S2−) and polysulfide (SADP-S n 2−), can supply additional electrons to improve the denitrification efficiency. However, the in-situ SADP process was challenging to control, resulting in the unstable enhancement efficiency and excessive sulfide emissions, thereby impeding its scalability in practical engineering. In this study, an independent SADP process was achieved in a sulfur-packed bed bioreactor, with a controllable sulfide production rate ranging from 0.24 ± 0.02 to 0.83 ± 0.03 kg-S/m3/d by adjusting the empty bed contact time between 1 and 5 h. Subsequently, the SADP bioreactor was connected upstream of a SADN bioreactor to create a sulfur-based autotrophic disproportionation-denitrification (SAD2) system. The SAD2 system realized an enhanced denitrification rate by up to 2.38 times, with flexibility to adjust between 0.65 ± 0.06–1.55 ± 0.20 kg-N/m3/d. One reason for this enhancement was that SADP-S2− provided additional electrons to the SADN process and exhibited higher biocompatibility than chemical-S2− (Na 2 S) at similar doses. Additionally, it stimulated the sulfur bioavailability by 1.66 times as a result of stoichiometry matrix calculation. SADP-S n 2− was only detected in the biofilm, as indicated by a linear increase in the S n proportion from 8.1 % to 30.1 %, but with minimal releases (352 μg-S/L) into the water. Another reason for the enhancement was bioaugmentation, with increases in protein (30.0 %), ATP (6.9 %), live cells proportion (10.1 %) and total relative abundance of denitrificans (87.7 %). These findings imply that the novel SAD2 system facilitates adjustable and high-rate nitrogen removal without the risk of sulfide emission, surpassing the capabilities of the independent SADN system. This offers a new pattern for practical applications. [ABSTRACT FROM AUTHOR]

The lowest energy structures of Au and AuNi ( = 2-9) clusters have been researched using the CALYPSO structure searching method in conjunction with the density functional theory. It is found that the most stable structures of Au, Au8Ni and Au9Ni clusters reported by Tang et al. [C. M. Tang, X. X. Chen and X. D. Yang, Int. J. Mod. Phys. B 28, 1450138 (2014)] are low-lying isomers. The correct ground states and vibrational spectra are given in this paper. [ABSTRACT FROM AUTHOR]