Extinction drives a discontinuous temporal pattern of species-area relationships in a microbial microcosm system.

As the most potential ecological "law", the mechanism of the species-area relationship (SAR) remains controversial. Essentially, the SAR addresses the relationship between regional area and biodiversity, shaped by speciation, extinction and dispersal processes. Extinction is the process of loss and a direct cause of species richness differences in community. Therefore, it is crucial to elucidate the role of extinction in shaping SAR. Since the extinction process has temporal dynamics, we propose the hypothesis that the occurrence of SAR should also have temporal dynamics. Here, we designed independent closed microcosm systems, in which dispersal/speciation can be excluded/neglected to reveal the role of extinction in shaping the temporal dynamics pattern of SAR. We find that extinction can shape SAR in this system independent of the dispersal and speciation process. Due to the temporal dynamics of the extinction, SAR was temporally discontinuous. The small-scale extinctions modified community structure to promote ecosystem stability and shaped SAR, while mass extinction pushed the microcosm system into the next successional stage and dismissed SAR. Our result suggested that SAR could serve as an indicator of ecosystem stability; moreover, temporal discontinuity can explain many controversies in SAR studies.

Synthesis of graphene oxide grafted by diazanyl groups and its application in recovery of lead from lead-acid wastewater.

Heavy metal ion (HMI) in wastewater is a kind of resource that is wrongly placed. Recovery of heavy metal from lead-acid wastewater desires efficient and reusable functional materials. In this paper, graphene oxide-like with diazanyl groups (GOLA) was synthesized by a nucleophilic substitution reaction of graphene oxide-like with hydroxyl groups (GOLH) with diazane. GOLA exhibited good stability and recyclability in wastewater. The maximal adsorption capacity (qmax) values of GOLA for Pb(II), Cd(II), Cu(II), Ni(II), and Cr(III) ions were 505.80, 401.99, 83.48, 82.29, and 147.77 mg/g, respectively. The equilibrium time of GOLA adsorbing HMIs was 20 min. GOLA was employed to recover lead ions from lead-acid wastewater to give Pb(OH)2 and reusable water. Therefore, this paper provides a useful method of recycling lead from lead-acid wastewater.

Study on degrading graphene oxide in wastewater under different conditions for developing an efficient and economical degradation method.

With popular application of graphene and graphene oxide (GO), they have been discharged into water. Graphene and GO harm organisms. However, an efficient and economical method for removing graphene and GO in wastewater has seldom been reported. Graphene can be oxidized by hydrogen peroxide to give GO; therefore, degradation of graphene oxide is an important step in the procedure of removal of graphene from water. In this paper, GO degradation via photo-Fenton reaction under different conditions was carried out. Experimental results suggested that GO in wastewater can be efficiently and economically degraded into carbon dioxide and H2O when pH value is 3, concentration of H2O2 and FeCl3 are 35 mM and 5 ppm, respectively. Degradation mechanism of GO was suggested based on UV-vis absorption spectra, scanning electron microscopy, X-ray diffraction and liquid chromatography-mass spectra data of degradation intermediates. This paper suggests an efficient and economical degradation way of GO in wastewater.

An efficient and environment-friendly method of removing graphene oxide in wastewater and its degradation mechanisms.

Graphene and graphene oxide (GO) have already existed in air, water and soil due to their popular application in functional materials. However, degradation of graphene and GO in wastewater has not been reported. Degradation of GO plays a key role in the elimination of graphene and GO in wastewater due to graphene being easily oxidized to GO. In this paper, GO was completely degraded to give CO2 by Photo-Fenton. The degradation intermediates were determined by UV-vis absorption spectra, elemental analysis (EA), fourier transform infrared (FT-IR) and liquid chromatography-mass spectrometry (LC-MS). Experimental results showed that graphene oxide was completely degraded to give CO2 after 28 days. Based on UV, FT-IR, LC-MS spectra and EA data of these degradation intermediates, the degradation mechanisms of GO were supposed. This paper suggests an efficient and environment-friendly method to degrade GO and graphene.

Electric response of a metal-molecule-metal junction to laser pulse by solving hierarchical equations of motion.

We have combined the quantum dissipative theory and the time dependent density functional theory to perform the first principle calculation of laser induced quantum dynamical electron transport through a molecule weak bridged to two electrodes. The formalism of hierarchical equations of motion based on non-equilibrium Green's function theory has been taken in this work. Numerical simulations of optical absorption spectra of benzene, laser induced transient current without and with bias, charge pumping effect, as well as the spectrum analysis from the current in Au-benzene-Au molecular junction are presented and discussed.

Reaction pathway investigation on the selective catalytic reduction of NO with NH3 over Cu/SSZ-13 at low temperatures.

The mechanism of the selective catalytic reduction of NO with NH3 was studied using Cu/SSZ-13. The adspecies of NO and NH3 as well as the active intermediates were investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy and temperature-programmed surface reaction. The results revealed that three reactions were possible between adsorbed NH3 and NOx. NO2(-) could be generated by direct formation or NO3(-) reduction via NO. In a standard selective catalytic reduction (SCR) reaction, NO3(-) was hard to form, because NO2(-) was consumed by ammonia before it could be further oxidized to nitrates. Additionally, adsorbed NH3 on the Lewis acid site was more active than NH4(+). Thus, SCR mainly followed the reaction between Lewis acid site-adsorbed NH3 and directly formed NO2(-). Higher Cu loading could favor the formation of active Cu-NH3, Cu-NO2(-), and Cu-NO3(-), improving the SCR activity at low temperature.

Two-photon resonant hyperpolarizability of an H-shaped molecule studied by wavelength-tunable hyper-Rayleigh scattering.

Wavelength dependent hyper-Rayleigh scattering measurements have been performed by using a fluorescence spectrometer. With this detection strategy, first molecular hyperpolarizability (ß) of a dual charge-transfer (H-shaped) chromophore and its monomer have been measured in two-photon resonance range from 670 to 950 nm as well as at off-resonance of 1064 nm. The absorption and resonance hyper-Rayleigh profiles can be simulated reasonably well with a common set of parameters. In addition, both resonance and off-resonance results show that ß(0) per chromophore has a remarkable enhancement for the H-shaped molecule as large as 1.7, compared with that of the monomer, which could be ascribed to two physical effects: (1) coherent enhancement of two chromophores and (2) intramolecular dipole-dipole interaction, which was confirmed by their fluorescence-decay behaviors.

Significant effect of bromo substituents on nonlinear optical properties of polymer and chromophores.

Four chromophores containing bromo substituents, a ployimide with bromo-containing chromophores, four reference functional polyimides, and fourteen reference chromophores were synthesized for studying effect of bromo substituents on nonlinear optical (NLO) properties of materials and chromophores. The results of hyper-Rayleigh scattering and UV-vis spectra show that static first molecular hyperpolarizability (beta(0)) values of bromo-containing chromophores are 1.24-5.75 times as beta(0) of the corresponding chloro-containing chromophores (Hammett constants sigma of chloro and bromo groups are same) without causing a visible shift of the absorption band to longer wavelength. UV-vis spectra and the results of Maker Fringe method show that the polyimide with chromophores containing bromo substituents exhibits a good optical transparency and a much higher macroscopic nonlinear optical coefficient (d(33) = 20.1 pm/V) than the reference polyimides containing nitro (d(33) = 9.6 pm/V) and cyano (d(33) = 8.9 pm/V) groups in spite of nitro and cyano groups being strong electron acceptors. d(33) of polyimide with chloro-containing chromophores is very small. Therefore, this paper suggests an effective strategy for improving the NLO properties of polymeric materials and chromophores without reducing optical transparency in designing NLO polymers and chromophores. On the basis of quantum chemistry calculations, the reasons of effect of bromo substituents on NLO properties of chromophores and materials were discussed.

Theoretical study of nonlinear optical properties of "parallel connection" chromophores containing parallel nonconjugated D-pi-A units.

Chromophores containing two parallel nonconjugated D-pi-A units are effective chromophores with high hyperpolarizability and good optical transparency. It provides a method for the design and synthesis of effective chromophores. The semiempirical method ZINDO was employed to study the relationship between enhancement of the static first hyperpolarizabilities (beta0) per D-pi-A unit and the number of parallel nonconjugated D-pi-A units in a chromophore. The results show that the chromophores containing two parallel nonconjugated D-pi-A units would exhibit higher beta0 values than two times the beta0 value of the corresponding reference chromophore containing a D-pi-A unit. The chromophore containing three parallel nonconjugated D-pi-A units exhibits the highest enhancement of beta0 per D-pi-A unit, which is 10.1 times the beta0 value of the corresponding reference chromophore. However, the beta0 value of the chromophore containing four parallel nonconjugated D-pi-A units is very small, and the enhancement of beta0 value per D-pi-A unit decreases sharply, from 10.1 to 0.3, with increasing the number of parallel D-pi-A units in a chromophore from 3 to 4. It could give a useful suggestion for designing chromophores containing parallel nonconjugated D-pi-A units.