Heterogeneous Fenton‐like reactions (HFLR) are promising alternative strategies to address the inherent limitations of the classic Fenton systems. Herein, a facile and scale‐up approach for the ...synthesis of transition metal single‐atom sites (SA‐TM, TM = Cr, Mn, Fe, Co, Cu) coordinated onto pyrrolic N‐rich g‐C3N4 (PN‐g‐C3N4) scaffold is developed. The regulated pyrrolic N‐rich SA‐TM catalytic sites exhibit excellent performances for HFLR. As a model of SA‐TM/PN‐g‐C3N4, SA‐Cr/PN‐g‐C3N4 is efficient for the catalytic oxidation of bisphenol A via HFLR under visible light with outstanding cyclic stability and wide effective pH range (3.0–11.0). The synergy of photocatalysis and single‐atom catalysis leads to accelerated production and separation of charge carriers as well as the cycling of Cr3+/Cr2+ couple, consequently boosting the performance in HFLR. Theoretical calculations indicate that the Cr(II)‐N4 sites with the metalloporphyrin‐like structure are more reactive than the doped Cr(II) sites in the g‐C3N4 matrix, which act as the peroxidase‐mimicking nanozyme for efficient and homolytic cleavage of peroxide OO in H2O2. This study expands the family of the iron‐free Fenton‐like systems and provides new strategies to the rational design and precise regulation of on‐demand multifunctional single‐atom catalysts for advanced water remediation.
Synergistic catalysis induced by transition metal single‐atom sites coordinated onto pyrrolic N‐rich graphitic carbon nitride leads to an outstanding performance toward the photocatalytic Fenton‐like reaction with outstanding cyclic stability and a wide effective pH range.
Composites‐based photocatalysis relies on the interfacial electron transfer between the metallic cocatalyst and photosensitizer (the semiconductor) to realize spatial separation of charge carriers. ...Herein, an ingenious heterojunction between Co‐CN single atom catalysts (SACs) and g‐C3N4 is constructed for heterogeneous photo‐Fenton‐like reactions. Driven by built‐in electric field across the heterojunctions, the separation and migration of the photogenerated charge carriers is promoted, leading to the fast electron transfer from the g‐C3N4 to the Co‐CN SACs. Theoretical calculations and transient absorption spectroscopy reveal the modulated charge transfer and trapping in the SA‐Co‐CN/g‐C3N4 heterostructure, resulting in the remarkably enhanced generation of reactive oxygen species via peroxymonosulfate activation under light irradiation. This ingenious SA‐Co‐CN/g‐C3N4/PMS/vis system is efficient for the oxidation of various antibiotics with high removal efficiency (>98%), a wide operating pH range (pH 3–11) and excellent stability in long‐term operation. This study provides a new tactic for rational design of SACs‐based heterojunctions to bridge photocatalysis and heterogeneous catalysis, attaining superior photoredox activity via interfacial coupling.
Heterojunction between island‐like Co single‐atom catalyst and g‐C3N4 is constructed and shows the modulated charge transfer and trapping behavior. Driven by the strong built‐in electric filed across the heterojunction, the cascade electron transfer from g‐C3N4 to Co single sites leads to an enhanced performance for generation of radical reactive oxygen species via the photo‐Fenton‐like reaction.
Stochastic gradient descent (SGD) still is the workhorse for many practical problems. However, it converges slow, and can be difficult to tune. It is possible to precondition SGD to accelerate its ...convergence remarkably. But many attempts in this direction either aim at solving specialized problems, or result in significantly more complicated methods than SGD. This paper proposes a new method to adaptively estimate a preconditioner, such that the amplitudes of perturbations of preconditioned stochastic gradient match that of the perturbations of parameters to be optimized in a way comparable to Newton method for deterministic optimization. Unlike the preconditioners based on secant equation fitting as done in deterministic quasi-Newton methods, which assume positive definite Hessian and approximate its inverse, the new preconditioner works equally well for both convex and nonconvex optimizations with exact or noisy gradients. When stochastic gradient is used, it can naturally damp the gradient noise to stabilize SGD. Efficient preconditioner estimation methods are developed, and with reasonable simplifications, they are applicable to large-scale problems. Experimental results demonstrate that equipped with the new preconditioner, without any tuning effort, preconditioned SGD can efficiently solve many challenging problems like the training of a deep neural network or a recurrent neural network requiring extremely long-term memories.
Single-atom Cu catalytic sites supported on reduced graphene oxide exhibited an enhanced performance toward the activation of peroxymonosulfate.
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•Single-atom Cu (SA-Cu) supported on ...reduced graphene oxide (rGO) was fabricated.•The SA-Cu/rGO exhibited better performance for the activation of PMS than pure rGO.•Sulfamethoxazole was efficient removed in the SA-Cu/rGO/PMS system.•The SO4− and OH radicals as well as 1O2 were the main reactive species.
Single metal catalysts build a bridge between homogeneous catalysis and heterogeneous catalysis. Herein, we report the single-atom copper sites embedded in reduced graphene oxide (SA-Cu/rGO) for the degradation of various antibiotics, including sulfamethoxazole (SMX), meropenem and sulfafurazole via the heterogeneous activation of peroxymonosulfate (PMS). The SA-Cu/rGO/PMS system exhibited an enhanced performance toward the degradation of SMX with the kinetic was ~3.9 times faster than in the rGO/PMS system. Strikingly, we found that over 99% of the total organic carbon (TOC) was eliminated in the SA-Cu/rGO/PMS system within 120 min, demonstrating its excellent mineralization ability. The enhanced catalytic performance could be due to the synergistic effect between the rGO matrix and the exposed Cu active sites, which facilitated the generation large amount of reactive species and the in-situ decomposition of the pollutants at the surface of the catalysts. This SA-Cu/rGO catalyst with multifunctional properties can be potentially applied in the treatment of refractory wastewater.
Abstract
Heterogeneous Fenton‐like reactions (HFLR) are promising alternative strategies to address the inherent limitations of the classic Fenton systems. Herein, a facile and scale‐up approach for ...the synthesis of transition metal single‐atom sites (SA‐TM, TM = Cr, Mn, Fe, Co, Cu) coordinated onto pyrrolic N‐rich g‐C
3
N
4
(PN‐g‐C
3
N
4
) scaffold is developed. The regulated pyrrolic N‐rich SA‐TM catalytic sites exhibit excellent performances for HFLR. As a model of SA‐TM/PN‐g‐C
3
N
4
, SA‐Cr/PN‐g‐C
3
N
4
is efficient for the catalytic oxidation of bisphenol A via HFLR under visible light with outstanding cyclic stability and wide effective pH range (3.0–11.0). The synergy of photocatalysis and single‐atom catalysis leads to accelerated production and separation of charge carriers as well as the cycling of Cr
3+
/Cr
2+
couple, consequently boosting the performance in HFLR. Theoretical calculations indicate that the Cr(II)‐N
4
sites with the metalloporphyrin‐like structure are more reactive than the doped Cr(II) sites in the g‐C
3
N
4
matrix, which act as the peroxidase‐mimicking nanozyme for efficient and homolytic cleavage of peroxide OO in H
2
O
2
. This study expands the family of the iron‐free Fenton‐like systems and provides new strategies to the rational design and precise regulation of on‐demand multifunctional single‐atom catalysts for advanced water remediation.
The convergence of green growth is not only very important for the sustainable development of mankind, but also plays a key role in the coordinated development of eastern, Midwest regions of China. ...The effect of innovative human capital (IHC) on the convergence of regional green growth in China needs to be explored. This paper empirically explores the impact of IHC on the convergence of regional green growth in China from spatial perspective for the first time. Through the regression analysis of the convergence models, three main conclusions are obtained: (1) there are obvious conditional β space convergence characteristics of green growth among inter-provincial units in China. Under the spatial correlation expressed by distance weights and adjacent weights, the conditional β space convergence characteristics of green growth are quite different. (2) Compared with the adjacency weight, under the distance weight, the spatial diffusion effect of innovative knowledge and technologies created by IHC is stronger. (3) There is club convergence of green growth in the East and the Midwest regions, and the quantity and quality of IHC in the Midwest region play a stronger role in the convergence of green growth than in the East region. Based on the above conclusions, this paper proposes some policies for the East and Midwest regions.
While molecular weight distribution (MWD) is one of the most important properties of soluble microbial products (SMPs), mechanisms underlying effects of MWD of SMPs on membrane fouling have not well ...unveiled. In this study, it was found that, the supernatant of sludge suspension in a membrane bioreactor (MBR) for wastewater treatment can be fractionated into a series of SMPs samples with different molecular weight (MW) fraction. The real gel sample mainly formed by the rejected SMPs on membrane surface had a high specific filtration resistance (SFR) of 1.21 × 1016 m−1 kg−1. The SFR of SMPs samples and the model foulants of polyethylene glycol (PEG) increased with their MW. The change trend of SFR with MW cannot be sufficiently explained by three-dimensional excitation-emission matrix (EMM) and chemical compositions. Tyndall effect analysis indicated that gelating ability of SMPs and PEG in the solution increased with their MW. Scanning electron microscope (SEM) confirmed gel structure changes with the PEG MW. Accordingly, mechanisms based on Carman–Kozeny equation and Flory–Huggins lattice theory were proposed to interpret SFR of SMPs with low and high MW, respectively. Simulating these two mechanistic models on PEG samples resulted in the comparable SFR data to the experimental ones, indicating the correctness and feasibility of the proposed mechanisms. The proposed mechanisms provided in-depth understanding of membrane fouling regarding MW, facilitating to develop effective membrane fouling mitigation strategies.
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•Specific filtration resistance (SFR) of SMPs increased with molecular weight (MW).•Gelating ability of SMPs and PEG in the solution increased with their MW.•Carman–Kozeny equation based mechanism governed SFR of SMPs with low MW.•Flory–Huggins lattice theory well explained SFR of SMPs with high MW.
The COVID-19 outbreak has shocked the world's economies in the year of 2020. As this pandemic spreads around the globe, many experts feared that the global food supplies might start running short, ...especially if supply chains were disrupted. COVID-19 also added to the uncertainty of the business operation. Therefore, it is critical to understand how COVID-19 pandemic affected global food supply and market. In this study, we investigate the impact of COVID-19 on agricultural export companies in China using a unique firm-level survey data. We found that although on average agricultural businesses experienced declines in the exports, exports of some agricultural products especially grain and oil held strong and even increased, implying the essential demand for staple food during the pandemic. Not surprisingly, exports of medicinal herb also increased significantly during the pandemic. However, exports of goods such as edible fungus and horticultural products sharply decreased. Our results also showed that in general, impact of COVID-19 on smaller firms was more severe than that on larger firms. The results of this study can provide useful guidance and implications for agricultural businesses and policy makers on their COVID-19 mitigation efforts to navigate this global pandemic.
In this paper, we consider the joint blind source separation (JBSS) problem and introduce a number of algorithms to solve the JBSS problem using the independent vector analysis (IVA) framework. ...Source separation of multiple datasets simultaneously is possible when the sources within each and every dataset are independent of one another and each source is dependent on at most one source within each of the other datasets. In addition to source separation, the IVA framework solves an essential problem of JBSS, namely the identification of the dependent sources across the datasets. We propose to use the multivariate Gaussian source prior to achieve JBSS of sources that are linearly dependent across datasets. Analysis within the paper yields the local stability conditions, nonidentifiability conditions, and induced Cramér-Rao lower bound on the achievable interference to source ratio for IVA with multivariate Gaussian source priors. Additionally, by exploiting a novel nonorthogonal decoupling of the IVA cost function we introduce both Newton and quasi-Newton optimization algorithms for the general IVA framework.
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