Stereoselective synthesis of novel functionalized cyclohexanone derivatives via the condensation of aromatic aldehydes with acetoacetamide and the influence of the ortho-effect and autocondensation

A simple, inexpensive and stereoselective synthesis of novel functionalized cyclohexanone derivatives via the reaction of acetoacetamide with aromatic aldehydes in ethanol at room temperature is described. Additionally, the presence of substituents such as NO₂ and Cl in the ortho-position of the aldehyde aromatic ring resulted in the formation of novel piperidines. The use of Lewis acids such as iron(III) chloride and bismuth(III) nitrate as catalysts led to autocondensation of acetoacetamide and the formation of 2,4-dimethyl-6-oxo-1,6-dihydropyridine-3-carboxamide.     

Effects of exogenic chloride on oxidative degradation of chlorinated azo dye by UV-activated peroxodisulfate

Recently, the degradation of organic compounds in saline dye wastewater by sulfate radicals (SO₄⁻)-based advanced oxidation processes (AOPs) have attracted much attention. However, previous studies on these systems have selected non-chlorinated dyes as model compounds, and little is known about the transformation of chlorinated dyes in such systems. In this study, acid yellow 17 (AY-17) was selected as a model of chlorinated contaminants, and the degradation kinetics and evolution of oxidation byproducts were investigated in the UV/PDS system. AY-17 can be efficiently degraded (over 98% decolorization) under 90 min irradiation at pH 2.0–3.0, and the reaction follows pseudo-first order kinetics. Cl^‒ accelerated the degradation of AY-17, but simultaneously led to an undesirable increase of absorbable organic halogen (AOX). Several chlorinated byproducts were identified by liquid chromatography-mass spectrometry (LC–MS/MS) in the UV/PDS system. It indicates that endogenic chlorine and exogenic Cl^– reacted with SO₄⁻ to form chloride radicals, which are involved in the dechlorination and rechlorination of AY-17 and intermediates. The possible degradation mechanisms of AY-17 photooxidative degradation are proposed. This work provides valuable information for further studies on the role of exogenic chloride in the degradation of chlorinated azo dyes and the kinetic parameters in the PDS-based oxidation process.     

Structural elucidation of a methylenation reagent of esters: synthesis and reactivity of a dinuclear titanium(iii) methylene complex

Transmetallation of a zinc methylene complex [ZnI(tmeda)]₂(μ-CH₂) with a titanium(iii) chloride [TiCl₃(tmeda)(thf)] produced a titanium methylene complex. The X-ray diffraction study displayed a dinuclear methylene structure [TiCl(tmeda)]₂(μ-CH₂)(μ-Cl)₂. Treatment of an ester with the titanium methylene complex resulted in methylenation of the ester carbonyl to form a vinyl ether. The titanium methylene complex also reacted with a terminal olefin, resulting in olefin-metathesis and olefin-homologation. Cyclopropanation by methylene transfer from the titanium methylene proceeded by use of a 1,3-diene. The mechanistic study of the cyclopropanation reaction by the density functional theory calculations was also reported.

Transmetallation of a zinc methylene complex [ZnI(tmeda)]₂(μ-CH₂) with a titanium(iii) chloride [TiCl₃(tmeda)(thf)] produced a titanium methylene complex.     

The role of 8-quinolinyl moieties in tuning the reactivity of palladium(II) complexes: a kinetic and mechanistic study

The rate and mechanism of chloride substitution from Pd(II) complexes, chlorobis-(2-pyridylmethyl)aminepalladium(II), 1, chloro-8-[(2-pyridylmethyl)amino]quinolinepalladium(II), 2, chloro-N-(2-pyridinylmethylene)-8-quinolinaminepalladium(II), 3, and chlorobis(8-quinolinyl)aminepalladium(II), 4, are reported. The labile chloride was substituted from the complexes by thiourea nucleophiles viz, thiourea (Tu), N,N′-dimethylthiourea (Dmtu) and N,N,N′,N′-tetramethylthiourea (Tmtu). The reactions were monitored under pseudo-first-order conditions in methanol using stopped-flow spectrophotometry as a function of concentration and temperature. All the reactions obeyed the rate law k_obs = k₂[Nu] following the order 1 > 3 > 2 > 4 with 4 exhibiting the slowest rate of substitution due to the stronger σ-donor effect of 8-quinolyl moiety of the coordinated ligand, which makes the Pd center more electron-rich. This slows the nucleophilic attack by the nucleophiles. The values of the thermodynamic parameters (ΔH^# and ΔS^#) support an associative substitution mechanism. The trends in the DFT calculated data support the experimentally observed order of the reactivity of the complexes.

     

An Artificial Single Molecular Channel Showing High Chloride Transport Selectivity and pH-Responsive Conductance

Inspired by the unique structure and function of the natural chloride channel (ClC) selectivity filter, we present herein the design of a ClC-type single channel molecule. This channel displays high ion transport activity with half-maximal effective concentration, EC₅₀, of 0.10 μM, or 0.075 mol % (channel molecule to lipid ratio), as determined by fluorescent analysis using lucigenin-encapsulated vesicles. Planar bilayer lipid membrane conductance measurements indicated an excellent Cl⁻/K⁺ selectivity with a permeability ratio P /P up to 12.31, which is comparable with the chloride selectivity of natural ClC proteins. Moreover, high anion/anion selectivity (P /P =66.21) and pH-dependent conductance and ion selectivity of the channel molecule were revealed. The ClC-like transport behavior is contributed by the cooperation of hydrogen bonding and anion–π interactions in the central macrocyclic skeleton, and by the existence of pH-responsive terminal phenylalanine residues.     

Assessment of DFT based optimized molecular structure-antioxidant efficacy relationship of trimethylgermanium(IV) complexes

Optimized molecular structure-antioxidant efficacy relationship of trimethylgermanium(IV) complexes involving biologically active bulky heterocyclic-O-donor ligands was investigated using density functional theory (DFT). The complexes

where R = -CH₂CH₃[L₍₁₎H],-C₆H₅[L₍₂₎H], p-ClC₆H₄-[L₍₃₎H] were prepared by the reaction of trimethylgermanium chloride with sodium salts of bulky heterocyclic-O-donor ligands in 1:1 M ratio in refluxing dry THF. The complexes were characterized by various spectroscopic techniques namely FTIR, ¹H and ¹³C NMR. The spectral evidences are indicative of a bidentate behaviour of the ligands in these complexes which adopt a pentacoordinated geometry. Computational studies of these complexes have been carried out using B3LYP/6-31G* basis set to obtain molecular geometry, ground state energy and other global reactivity parameters. The most stable geometry having lowest optimized energy was chosen and bond lengths and bond angles were computed. The HOMO-LUMO energies for the complexes have been computed in order to ascertain the energy distribution and reactivity behaviour. These complexes were evaluated for antioxidant activity using FRAP (ferric reducing antioxidant power) assay and demonstrated potential antioxidant activity of distinguishable magnitude.     

Mono-silicon isoelectronic replacement in CAl4: van't hoff/le bel carbon or not?

In cluster studies, the isoelectronic replacement strategy has been successfully used to introduce new elements into a known structure while maintaining the desired topology. The well-known penta-atomic 18 valence electron (ve) species and its Al⁻/Si or Al/Si⁺ isoelectronically replaced clusters CAl₃Si⁻, CAl₂Si₂, , and , all possess the same anti-van't Hoff/Le Bel skeletons, that is, nontraditional planar tetracoordinate carbon (ptC) structure. In this article, however, we found that such isoelectronic replacement between Si and Al does not work for the 16ve-CAl₄ with the traditional van't Hoff/Le Bel tetrahedral carbon (thC) and its isoelectronic derivatives CAl₃X (X = Ga/In/Tl). At the level of CCSD(T)/def2-QZVP//B3LYP/def2-QZVP, none of the global minima of the 16ve mono-Si-containing clusters CAl₂SiX⁺ (X = Al/Ga/In/Tl) maintains thC as the parent CAl₄ does. Instead, X = Al/Ga globally favors an unusual ptC structure that has one long C─X distance yet with significant bond index value, and X = In/Tl prefers the planar tricoordinate carbon. The frustrated formation of thC in these clusters is ascribed to the CSi bonding that prefers a planar fashion. Inclusion of chloride ion would further stabilize the ptC of CAl₂SiAl⁺ and CAl₂SiGa⁺. The unexpectedly disclosed CAl₂SiAl⁺ and CAl₂SiGa⁺ represent the first type of 16ve-cationic ptCs with multiple bonds. © 2019 Wiley Periodicals, Inc.     

Preparation of a porphyrin-polyoxometalate hybrid and its photocatalytic degradation performance for mustard gas simulant 2-chloroethyl ethyl sulfide

By combining 5,10,15,20-tetra（4-chlorine）phenylporphyrin（TClPP） and α-Keggin polyoxometalate H₅PV₂Mo₁₀O₄₀（H₅PVMo） via a simple ion-exchange method, an organic-inorganic hybrid material[C₄₄H₂₈N₄Cl₄]_1.5[H₂PMo₁₀V₂O₄₀]·2C₂H₆O（H₂TClPP-H₂PVMo） was prepared and thoroughly characterized by a variety of techni...     

A single point mutation converts a proton-pumping rhodopsin into a red-shifted,turn-on fluorescent sensor for chloride

The visualization of chloride in living cells with fluorescent sensors is linked to our ability to design hosts that can overcome the energetic penalty of desolvation to bind chloride in water. Fluorescent proteins can be used as biological supramolecular hosts to address this fundamental challenge. Here, we showcase the power of protein engineering to convert the fluorescent proton-pumping rhodopsin GR from Gloeobacter violaceus into GR1, a red-shifted, turn-on fluorescent sensor for chloride in detergent micelles and in live Escherichia coli. This non-natural function was unlocked by mutating D121, which serves as the counterion to the protonated retinylidene Schiff base chromophore. Substitution from aspartate to valine at this position (D121V) creates a binding site for chloride. The binding of chloride tunes the pK_a of the chromophore towards the protonated, fluorescent state to generate a pH-dependent response. Moreover, ion pumping assays combined with bulk fluorescence and single-cell fluorescence microscopy experiments with E. coli, expressing a GR1 fusion with a cyan fluorescent protein, show that GR1 does not pump ions nor sense membrane potential but instead provides a reversible, ratiometric readout of changes in extracellular chloride at the membrane. This discovery sets the stage to use natural and laboratory-guided evolution to build a family of rhodopsin-based fluorescent chloride sensors with improved properties for cellular applications and learn how proteins can evolve and adapt to bind anions in water.

By utilizing laboratory-guided evolution, we have converted the fluorescent proton-pumping rhodopsin GR from Gloeobacter violaceus into GR1, a red-shifted, turn-on fluorescent sensor for chloride.     

Silica supported potassium oxide catalyst for dehydration of 2-picolinamide to form 2-cyanopyridine

The dehydration of 2-picolinamide to produce 2-cyanopyridine was investigated thoroughly using silica supported potassium oxide as a heterogeneous catalyst. Both large specific surface area and pore size of SiO_2 (B) contributed to the favorable catalytic performance for the synthesis of 2-CP. In addition, the yield of 2-CP showed the linear relationship with the amounts of medium basicity of the catalysts,demonstrating that medium basic sites were the active sites of silica supported potassium oxide catalysts. The catalysts were further characterized by XRD and FT-IR to clarify the active species. The results indicated the Si—O—K group produced by the reaction of K_2CO_3 with Si—OH was the active species, which was further evidenced by the adjustment of the amount of Si—OH by silylation and hydroxylation procedure.     

The Reaction of Muonium with Hydrogen Peroxide in Aqueous Solution

Rate constants for the reactions of muonium (Mu) (the ultralight isotope of the hydrogen atom) with H₂O₂ in H₂O and D₂O₂ in D₂O have been determined at various temperatures and pH (pD) values. The data are consistent with the three reactions: , , and the equivalent for the deuterated entities. A significant positive H/D isotope effect was found for the undissociated peroxide, while for the anions the effect was negligible or slightly in the opposite direction. In addition, for concentrated solutions of peroxide a study of the muon spin polarization as a function of applied transverse magnetic field yielded results consistent with the rate constants determined from the direct decay measurements, and indicated that the reaction products are diamagnetic, most likely MuH and MuOH, i. e., no muoniated radical products are formed. These results are potentially relevant for management of the radiolysis products in nuclear industry.     

The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and its Relevance in Solar Geoengineering Models

SO₂ has been proposed in solar geoengineering as a precursor of H₂SO₄ aerosol, a cooling agent active in the stratosphere to contrast climate change. Atmospheric ionization sources can ionize SO₂ into excited states of , which quickly reacts with trace gases in the stratosphere. In this work we explore the reaction of with excited by tunable synchrotron radiation, leading to ( ), where H contributes to O₃ depletion and OH formation. Density Functional Theory and Variational Transition State Theory have been used to investigate the dynamics of the title barrierless and exothermic reaction. The present results suggest that solar geoengineering models should test the reactivity of with major trace gases in the stratosphere, such as H₂ since this is a relevant channel for the OH formation during the nighttime when there is not OH production by sunlight. OH oxides SO₂, triggering the chemical reactions leading to H₂SO₄ aerosol.     

Rational Improvement of Single-Molecule Magnets by Enforcing Ferromagnetic Interactions

The anisotropy barrier of polynuclear single-molecule magnets is expected to be higher with less tunneling the better stabilized the spin ground state is so that less M_S mixing in the ground state and with excited spin states occur. We have realized this experimentally in two structurally related heptanuclear SMMs: the triplesalen-based [Mn^III ₆ Cr^III]³⁺ and the triplesalalen-based *[Mn^III ₆ Cr^III]³⁺ . The ligand system triplesalen was developed to enforce ferromagnetic interactions by the spin-polarization mechanism. However, we found weak antiferromagnetic couplings, that we assigned to an inefficient spin-polarization by a heteroradialene formation. To prevent this heteroradialene formation, the triplesalalen ligand H₆talalen was designed. Here, we present the building block [(talalen )Mn^III₃]³⁺ and its application for the assembly of [{(talalen )Mn^III₃}₂{Cr^III(CN)₆}]³⁺ (= *[Mn^III ₆ Cr^III]³⁺ ). Both the trinuclear and heptanuclear complexes are SMMs. The comparison to the related triplesalen complex [(feld )Mn^III₃]³⁺ proves the absence of heteroradialene character and the enforcement of ferromagnetic Mn^III-Mn^III interactions in the (talalen )⁶⁻ complexes. This results in an increase of the barrier for spin reversal U_eff from 25 K in the triplesalen-based [Mn^III ₆ Cr^III]³⁺ SMMs to 37 K in the triplesalalen-based *[Mn^III ₆ Cr^III]³⁺ SMM proving the success of our concept. Based on this study, the next step in the rational improvement of our SMMs is discussed.     

Extremal Wiener and Kirchhoff indices of globular caterpillars

The Wiener and Kirchhoff indices of a graph G are two of the most important topological indices in mathematical chemistry. A graph G is called to be a globular caterpillar if G is obtained from a complete graph K _s with vertex set {v₁,v₂,…, v _s} by attaching n _i pendent edges to each vertex v _i of K _s for some positive integers s and n₁,n₂,…,n _s, denoted by . Let be the set of globular caterpillars with n vertices (). In this article, we characterize the globular caterpillars with the minimal and maximal Wiener and Kirchhoff indices among , respectively.     

Supramolecular Assembly of Metal Complexes by (Aryl)I⋅⋅⋅d [PtII] Halogen Bonds

The theoretical data for the half-lantern complexes [{Pt( )(μ- )}₂] [ 1 – 3 ; is cyclometalated 2-Ph-benzothiazole; is 2-SH-pyridine ( 1 ), 2-SH-benzoxazole ( 2 ), 2-SH-tetrafluorobenzothiazole ( 3 )] indicate that the Pt ⋅⋅⋅ Pt orbital interaction increases the nucleophilicity of the outer d orbitals to provide assembly with electrophilic species. Complexes 1 – 3 were co-crystallized with bifunctional halogen bonding (XB) donors to give adducts ( 1 – 3 )₂ ⋅ (1,4-diiodotetrafluorobenzene) and infinite polymeric [ 1⋅ 1,1′-diiodoperfluorodiphenyl]_n. X-ray crystallography revealed that the supramolecular assembly is achieved through (Aryl)I ⋅⋅⋅ d [Pt^II] XBs between iodine σ-holes and lone pairs of the positively charged (Pt^II)₂ centers acting as nucleophilic sites. The polymer includes a curved linear chain ⋅⋅⋅ Pt₂ ⋅⋅⋅ I(arene^F)I ⋅⋅⋅ Pt₂ ⋅⋅⋅ involving XB between iodine atoms of the perfluoroarene linkers and (Pt^II)₂ moieties. The ¹⁹⁵Pt NMR, UV/Vis, and CV studies indicate that XB is preserved in CH(D)₂Cl₂ solutions.     

S(vi) in three-component sulfonamide synthesis: use of sulfuric chloride as a linchpin in palladium-catalyzed Suzuki–Miyaura coupling

Sulfuric chloride is used as the source of the –SO₂– group in a palladium-catalyzed three-component synthesis of sulfonamides. Suzuki–Miyaura coupling between the in situ generated sulfamoyl chlorides and boronic acids gives rise to diverse sulfonamides in moderate to high yields with excellent reaction selectivity. Although this transformation is not workable for primary amines or anilines, the results show high functional group tolerance. With the solving of the desulfonylation problem and utilization of cheap and easily accessible sulfuric chloride as the source of sulfur dioxide, redox-neutral three-component synthesis of sulfonamides is first achieved.

Sulfuric chloride is used as the source of the –SO₂– group in a palladium-catalyzed three-component synthesis of sulfonamides.

Since its development in the 1970s,¹ Suzuki–Miyaura coupling has become a widely used synthetic step in diverse areas. With two of the most widely sourced materials, organoborons and alkyl/aryl halides, a number of C–C coupling reactions are established and the Suzuki–Miyaura reaction has successfully acted as the key step in the synthesis of medicines and agrochemicals.²In addition to the well-known aryl halides and esters, various other substrates such as acid chlorides,³ anhydrides,⁴ diazonium salts⁵ and sulfonyl chlorides⁶ were also reported for the coupling in the past decades. As far as acid chlorides are concerned, carbamoyl chlorides were successfully transformed to the corresponding benzamides in the early years of the 21st century.⁷ However, the use of sulfamoyl chlorides as coupling partners is challenging due to the strong electron-withdrawing properties of the sulfonyl group, which cause the tendency of desulfonylation to form tertiary amines.Synthesis of sulfonyl-containing compounds, especially sulfones and sulfonamides, via the insertion of sulfur dioxide has been extensively studied during the last decade.⁸ A series of sulfur-containing surrogates have been developed as the source of the –SO₂– group. Willis and co-workers first reported the use of DABCO·(SO₂)₂, a bench-stable solid adduct of DABCO and gaseous SO₂ discovered by Santos and Mello,^9a as the source of sulfur dioxide in the synthesis of sulfonylhydrazines.^9b Soon after, alkali metal metabisulfites were found to provide sulfur dioxide for the formation of sulfonyl compounds.¹⁰ In the recent developments in this field, DABCO·(SO₂)₂ and metabisulfites have become the most popular SO₂ surrogates for the insertion of sulfur dioxide.⁸ However, the practical applications of sulfur dioxide insertion reactions are limited by atom-efficiency problems and the unique properties of reactants. For instance, the three-component synthesis of aryl sulfonylhydrazines using aryl halides, SO₂ surrogates and hydrazines by a SO₂-doped Buchward–Hartwig reaction was realized in the earliest developments in this field.¹⁰ However, similar transformations from aryl halides and amines to the corresponding sulfonamides still remain unresolved (Scheme 1a).^11,12Open in a separate windowScheme 1Synthetic approaches to sulfonamides.In order to provide a simple and efficient method for the three-component synthesis of aryl sulfonamides without the pre-synthesis of sulfonyl chlorides, many scientists have made various attempts. Interestingly, the use of arylboronic acids instead of aryl halides provided an alternative route. An oxidative reaction between boronic acids, DABCO·(SO₂)₂ and amines for the preparation of aryl sulfonamides at high temperature was realized,¹² while reductive couplings of boronic acids, SO₂ surrogates and nitroarenes were also reported (Scheme 1b).¹³ However, due to the reversed electronic properties of boronic acids from halides, additional additives and restrictions had to be considered. Extra oxidants and harsh conditions were usually used, and some of the transformations required “oxidative” substrates, such as nitroarenes and chloroamines.¹⁴Early in 2020, a reductive hydrosulfonamination of alkenes by sulfamoyl chlorides was reported,¹⁵ which gave us the inspiration to use in situ generated sulfamoyl chlorides as the electrophile for the synthesis of aryl sulfonamides by Suzuki–Miyaura coupling. In this way, sulfamoyl chlorides could be formed by nucleophilic substitution of an amine to sulfuric chloride, and the S(vi) central atom introduced into the reaction could reverse the electronic properties of the amine, which would eliminate the addition of oxidants (Scheme 1c). With the utilization of boronic acids as the coupling partner, a palladium-catalyzed Suzuki–Miyaura coupling could provide the sulfonamide products. Compared with traditional attempts, reversing the electronic properties of an amine from nucleophilic to electrophilic could reverse the whole reaction process, and two-step synthesis starting from the amine side could bypass the existing difficulty of S–N bond forming reductive elimination.¹² Instead, a C–S bond formation could be the key for success (Scheme 2). In this proposed route, the presence of a base would be essential to remove the acid generated in situ during the reaction process. Additionally, we expected that the addition of a ligand would improve the oxidative addition of Pd(0) to sulfamoyl chloride, thus leading to the desired sulfonamide product.Open in a separate windowScheme 2Comparison between the traditional route and designed work.As designed based on our assumption, we used a commercialized sulfamoyl chloride intermediate A, which would be generated from morpholine 1a and SO₂Cl₂, to start our early investigations. The results showed that the direct Suzuki–Miyaura coupling of sulfamoyl chloride intermediate A and 2-naphthaleneboronic acid 2a mostly led to the generation of byproduct 3a′ with traditional phosphine ligands added to the reaction, and the desired product 3a was obtained in poor yields (Table 1, entries 1 and 2). It is known that an electron-rich ligand would enhance the oxidative addition of Pd(0) to the electrophile, and the bulky factor would facilitate the reductive elimination process. As expected, the yield of product 3a was increased significantly when electron-rich and bulky tris-(2,6-dimethoxyphenyl)phosphine was used as the ligand (Table 1, entry 3). Moreover, the reaction could proceed more efficiently by using a mixture of THF and MeCN as the co-solvent (Table 1, entry 4).Early investigations using morpholine-4-sulfonyl chloride A as the starting material

Atomic-Scale Studies of Fe3O4(001) and TiO2(110) Surfaces Following Immersion in CO2-Acidified Water

Difficulties associated with the integration of liquids into a UHV environment make surface-science style studies of mineral dissolution particularly challenging. Recently, we developed a novel experimental setup for the UHV-compatible dosing of ultrapure liquid water and studied its interaction with TiO₂ and Fe₃O₄ surfaces. Herein, we describe a simple approach to vary the pH through the partial pressure of CO₂ ( ) in the surrounding vacuum chamber and use this to study how these surfaces react to an acidic solution. The TiO₂(110) surface is unaffected by the acidic solution, except for a small amount of carbonaceous contamination. The Fe₃O₄(001)-( × )R45° surface begins to dissolve at a pH 4.0–3.9 ( =0.8–1 bar) and, although it is significantly roughened, the atomic-scale structure of the Fe₃O₄(001) surface layer remains visible in scanning tunneling microscopy (STM) images. X-ray photoelectron spectroscopy (XPS) reveals that the surface is chemically reduced and contains a significant accumulation of bicarbonate (HCO₃⁻) species. These observations are consistent with Fe(II) being extracted by bicarbonate ions, leading to dissolved iron bicarbonate complexes (Fe(HCO₃)₂), which precipitate onto the surface when the water evaporates.     

Chitosan capped silver nanoparticles: Adsorption and photochemical activities

Chitosan capped silver nanoparticles (Chi-Ag) were prepared using AgNO₃ and sodium borohydride. Chitosan was detected by using ninhydrin test, thermal gravimetric analysis and measurement of relative viscosity. Chi-Ag was used for removal of cadmium (Cd²⁺) at room temperature. The maximum monolayer adsorption capacity, and sorption intensity were estimated to be 119.04 mg/g and 1.6, respectively, from Langmuir and Freundlich adsorption isotherm models. The kinetics of Cd²⁺ adsorption onto Chi-Ag was proceeds through the pseudo-second-order kinetic model. Boyd and Elovich models suggest the adsorption and/or coordination of Cd²⁺ with the NH₂ and OH groups of chitosan along with AgNPs proceeds through the film diffusion and chemisorption process. The average viscosity molecular weight of chitosan and Chi-Ag decreased with increased potassium persulfate (K₂S₂O₈) and hydrogen peroxide (H₂O₂) concentration. The presence of H₂O₂ and K₂S₂O₈ promoted the hydrolysis of chitosan due to the cleavage of glycosidic bond by generated HO and SO₄^? radicals.     

Functional groups to modify g-C_3N_4 for improved photocatalytic activity of hydrogen evolution from water splitting

Rational modification by functional groups was regarded as one of efficient methods to improve the photocatalytic performance of graphitic carbon nitride(g-C_3 N_4).Herein,g-C_3 N_4 with yellow(Y-GCN) and brown(C-GCN) were prepared by using the fresh urea and the urea kept for five years,respectively,for the first time.Experimental results show that the H2 production rate of the C-GCN is 39.06 μmol/h,which is about 5 times of the Y-GCN.Meantime,in terms of apparent quantum efficiency(AQ.E) at 420 nm,C-GCN has a value of 6.3% and nearly 7.3 times higher than that of Y-GCN(0.86%).The results of XRD,IR,DRS,and NMR show,different from Y-GCN,a new kind of functional group of —N=CH— was firstly in-situ introduced into the C-GCN,resulting in good visible light absorption,and then markedly improving the photocatalytic performance.DFT calculation also confirms the effect of the —N=CH— group band structure of g-C_3N_4.Furthermore,XPS results demonstrate that the existence of —N=CH— groups in C-GCN results in tight interaction between C-GCN and Pt nanoparticles,and then improves the charge separation and photocatalytic performance.The present work demonstrates a good example of "defect engineering" to modify the intrinsic molecular structure of g-C_3N_4 and provides a new avenue to enhance the photocatalytic activity of g-C_3N_4 via facile and environmental-friendly method.