Mechanism of lead immobilization by oxalic acid-activated phosphate rocks

Lead （Pb） chemical fixation is an important environmental aspect for human health. Phosphate rocks （PRs） were utilized as an adsorbent to remove Pb from aqueous solution. Raw PRs and oxalic acid-activated PRs （APRs） were used to investigate the effect of chemical modification on the Pb-binding capacity in the pH range 2.0-5.0. The Pb adsorption rate of all treatments above pH 3.0 reached 90%. The Pb binding on PRs and APRs was pH-independent, except at pH 2.0 in activated treatments. The X-ray diffraction analysis confirmed that the raw PRs formed cerussite after reacting with the Pb solution, whereas the APRs formed pyromorphite. The Fourier Transform Infrared spectroscopy analysis indicated that carbonate （CO32-） in raw PRs and phosphate （PO43-） groups in APRs played an important role in the Pb-binding process. After adsorption, anomalous block-shaped particles were observed by scanning electron microscopy with energy dispersive spectroscopy. The X-ray photoelectron spectroscopy data further indicated that both chemical and physical reactions occurred during the adsorption process according to the binding energy. Because of lower solubility of pyromorphite compared to cerussite, the APRs are more effective in immobilizing Pb than that of PRs.

Constructing crystalline homophase carbon nitride S-scheme heterojunctions for efficient photocatalytic hydrogen evolution

The number of photogenerated carriers involved in the photocatalytic reaction is one of the main factors influencing the photocatalytic activity,and constructing S-scheme heterojunctions can significantly en-hance the migration of photogenerated carriers,which is regarded as an effective method.In this study,Au nanoparticles(NPs)-supported crystallized heptazine/triazine-based carbon nitride(AHTCN)S-scheme heterojunction photocatalysts are successfully prepared by photoreduction methods.Except for the Au NPs function as an electron mediator,the experiment results and DFT calculations demonstrate that the Fermi energy level of crystallized heptazine/triazine-based heterojunction(HTCN)is pulled down after anchoring Au NPs,and thus the electron transfer path of HTCN changed from Type II-scheme to S-scheme.Owing to S-scheme heterojunction,the optimal AHTCN-2(2 wt.%Au loaded)exhibits the best photocat-alytic hydrogen evolution with a production rate of 715.2μmol h^(−1)g^(−1),which significantly outperforms that of the HTCN.This work delivers a new strategy for the construction of S-scheme heterojunctions.

Facile synthesis of Fe single-atom porous photocatalysts via direct metal atomization achieving efficient photocatalytic nitrogen fixation

Photocatalytic nitrogen fixation has been explored as a feasible pathway for ammonia synthesis.How-ever,the convenient and efficient preparation of photocatalysts for nitrogen fixation remains a challenge.Meanwhile,the reaction pathway and mechanism of photocatalytic nitrogen fixation are unclear.Herein,single-atom Fe-porous g-C_(3)N_(4)(FPx)samples were manufactured using a one-step anneal technique via bubble template and direct metal atomization.Characterization results indicate that FPx has a porous structure and single-atom Fe.The porous structure exposed more active centers.Simultaneously,single-atom Fe changes the adsorption mode of N_(2)from physical to chemical and turns the photocatalytic ni-trogen fixation from the associative distal pathway to the associative alternating pathway.Consequently,without any sacrificial agent or cocatalysts,FPx presents a prominent increase in photocatalytic activ-ity,reaching 62.42μmol h^(−1)g^(−1),over fivefold larger than that of bulk g-C_(3)N_(4).This work provides new insights into photocatalytic nitrogen fixation and achieves efficient N_(2)photoreduction by constructing single-atom photocatalysts.