The Resource Utilization of Poplar Leaves for CO2 Adsorption.

Every late autumn, fluttering poplar leaves scatter throughout the campus and city streets. In this work, poplar leaves were used as the raw material, while H3PO4 and KOH were used as activators and urea was used as the nitrogen source to prepare biomass based-activated carbons (ACs) to capture CO2. The pore structures, functional groups and morphology, and desorption performance of the prepared ACs were characterized; the CO2 adsorption, regeneration, and kinetics were also evaluated. The results showed that H3PO4 and urea obviously promoted the development of pore structures and pyrrole nitrogen (N-5), while KOH and urea were more conductive to the formation of hydroxyl (-OH) and ether (C-O) functional groups. At optimal operating conditions, the CO2 adsorption capacity of H3PO4- and KOH-activated poplar leaves after urea treatment reached 4.07 and 3.85 mmol/g, respectively, at room temperature; both showed stable regenerative behaviour after ten adsorption-desorption cycles.

Effect of Additives on CO2 Adsorption of Polyethylene Polyamine-Loaded MCM-41.

Organic amine-modified mesoporous carriers are considered potential CO2 sorbents, in which the CO2 adsorption performance was limited by the agglomeration and volatility of liquid amines. In this study, four additives of ether compounds were separately coimpregnated with polyethylene polyamine (PEPA) into MCM-41 to prepare the composite chemisorbents for CO2 adsorption. The textural pore properties, surface functional groups and elemental contents of N for MCM-41 before and after functionalization were characterized; the effects of the type and amount of additives, adsorption temperature and influent velocity on CO2 adsorption were investigated; the amine efficiency was calculated; and the adsorption kinetics and regeneration for the optimized sorbent were studied. For 40 wt.% PEPA-loaded MCM-41, the CO2 adsorption capacity and amine efficiency at 60 °C were 1.34 mmol/g and 0.18 mol CO2/mol N, when the influent velocity of the simulated flue gas was 30 mL/min, which reached 1.81 mmol/g and 0.23 mol CO2/mol N after coimpregnating 10 wt.% of 2-propoxyethanol (1E). The maximum adsorption capacity of 2.16 mmol/g appeared when the influent velocity of the simulated flue gas was 20 mL/min. In addition, the additive of 1E improved the regeneration and kinetics of PEPA-loaded MCM-41, and the CO2 adsorption process showed multiple adsorption routes.

Crystal Structure, Photophysical Study, Hirshfeld Surface Analysis, and Nonlinear Optical Properties of a New Hydroxyphenylamino Meldrum's Acid Derivative.

The structural, photophysical, and vibrational properties of a new hydroxyphenylamino Meldrum's acid derivative, 3-((2-hydroxyphenylamino)methylene)-1,5-dioxaspiro[5.5]undecane-2,4-dione (HMD), were studied. The comparison of experimental and theoretical vibrational spectra can help understand basic vibration patterns and provides a better interpretation of IR spectra. The UV-Vis spectrum of HMD was computed using density functional theory (DFT)/B3LYP/6-311 G(d,p) basis set in the gas state, and the maximum wavelength was in accord with the experimental data. The molecular electrostatic potential (MEP) and Hirshfeld surface analysis confirmed O(1)-H(1A)···O(2) intermolecular hydrogen bonds in the HMD molecule. The natural bond orbital (NBO) analysis provided delocalizing interactions between π→π* orbitals and n→σ*/π* charge transfer transitions. Finally, the thermal gravimetric (TG)/differential scanning calorimeter (DSC) and the non-linear optical (NLO) properties of HMD were also reported.

Synthesis, Crystal Structures, and Density Functional Theory Studies of Two Salt Cocrystals Containing Meldrum's Acid Group.

Two salt cocrystals, C31H34N4O8 (DDD) and C17H20N2O8 (MDD), were synthesized and their structures were determined by single-crystal X-ray diffraction. DDD is made up of one (C13H13O8)- anion, one (C9H11N2)+ cation, and one 5,6-dimethyl-1H-benzo[d]imidazole molecule. MDD consists of one (C4H7N2)+ cation and one (C13H13O8)- anion. DDD and MDD belong to the monoclinic, P21/c space group and triclinic, P-1 space group, respectively. A 1D-chained structure of DDD was constituted by N-H···N and N-H···O hydrogen bonds. However, a 1D-chained structure of MDD was bridged by N-H···O hydrogen bonds. Their density functional theory-optimized geometric structures with a B3LYP/6-311G(d,p) basis set fit well with those of crystallographic studies. By calculating their thermodynamic properties, the correlation equations of C 0 p,m , S 0 m , H 0 m , and temperature T were obtained. By comparing the experimental electronic spectra with the calculated electronic spectra, it is found that the PBEPBE/6-311G(d,p) method can simulate the UV-Vis spectra of DDD and MDD. In addition, the fluorescence spectra in the EtOH solution analysis show that the yellowish-green emission occurs at 570 nm (λex = 310 nm) for DDD and the purplish-blue emission occurs at 454 nm (λex = 316 nm) for MDD.

Development of Low-Cost Porous Carbons through Alkali Activation of Crop Waste for CO2 Capture.

To achieve the "double carbon" (carbon peak and carbon neutrality) target, low-cost CO2 capture at large CO2 emission points is of great importance, during which the development of low-cost CO2 sorbents will play a key role. Here, we chose peanut shells (P) from crop waste as the raw material and KOH and K2CO3 as activators to prepare porous carbons by a simple one-step activation method. Interestingly, the porous carbon showed a good adsorption capacity of 2.41 mmol/g for 15% CO2 when the mass ratio of K2CO3 to P and the activation time were only 0.5 and 0.5 h, respectively, and the adsorption capacity remained at 98.76% after 10 adsorption-desorption cycle regenerations. The characterization results suggested that the activated peanut shell-based porous carbons were mainly microporous and partly mesoporous, and hydroxyl (O-H), ether (C-O), and pyrrolic nitrogen (N-5) functional groups that promoted CO2 adsorption were formed during activation. In conclusion, KOH- and K2CO3-activated P, especially K2CO3-activated P, showed good CO2 adsorption and regeneration performance. In addition, not only the use of a small amount of the activator but also the raw material of crop waste reduces the sorbent preparation costs and CO2 capture costs.

The development of activated carbon from corncob for CO2 capture.

The accumulation and incineration of crop waste pollutes the environment and releases a large amount of CO2. In this study, corncob crop waste was directly activated using solid KOH in an inert atmosphere to prepare porous activated carbon (AC) to capture CO2, and to introduce N-containing functional groups that favour CO2 adsorption, urea was mixed with corncob and KOH to prepare N-doped AC. The physical and chemical properties of the AC were characterized, and the effects of the mass ratio of KOH and urea to corncob, the activation temperature and time as well as regeneration were investigated to explore the optimal preparation process. The pores in the AC are mainly micropores, with the specific surface area and pore volume reaching 926.07 m2 g-1 and 0.40 cm3 g-1 for KOH-activated corncob and 1096.70 m2 g-1 and 0.48 cm3 g-1 after N-doping; the C-O plus O-H ratio and the -NH- ratio, which favour CO2 adsorption in N-doped AC were 6.04 and 1.92%, respectively. The maximum adsorption capacities for KOH-activated corncob before and after N-doping were 3.49 and 4.58 mmol g-1, respectively, at 20 °C and remained at 3.44 and 4.52 mmol g-1 after ten regenerations. The prepared corncob-based AC showed good application prospects for CO2 capture.

3-(4-Fluoro-benzyl-idene)-1,5-dioxa-spiro-[5.5]undecane-2,4-dione.

In the title mol-ecule, C(16)H(15)FO(4), the fused 1,3-dioxane and cyclo-hexane rings exhibit a bath and a chair conformation, respectively. In the crystal, weak inter-molecular C-H⋯O hydrogen bonds link the mol-ecules into centrosymmetric dimers.

3-(4-Bromo-benzyl-idene)-1,5-dioxaspiro-[5.5]undecane-2,4-dione.

The title mol-ecule, C(16)H(15)BrO(4), was prepared by the reaction of (R)-2,4-dioxo-1,5-dioxaspiro-[5.5]undecane and 4-bromo-benzaldehyde with ethanol. The 1,3-dioxane ring exhibits a distorted boat and the fused cyclo-hexane ring exhibits a chair conformation.

2,2-Dimethyl-5-[(5-methyl-furan-2-yl)methyl-idene]-1,3-dioxane-4,6-dione.

The asymmetric unit of the title compound, C(12)H(12)O(5), contains two independent mol-ecules. In each, the 1,3-dioxane ring adopts an envelope conformation with the dimethyl-substituted C atom forming the flap. The crystal structure is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

5-(3,4-Dimethyl-benzyl-idene)-2,2-dimethyl-1,3-dioxane-4,6-dione.

The title compound, C(15)H(16)O(4), was prepared by the reaction of 2,2-dimethyl-1,3-dioxane-4,6-dione and 3,4-dimethyl-benzaldehyde in ethanol. The 1,3-dioxane ring exhibits an envelope conformation. In the crystal, mol-ecules are linked by weak inter-molecular C-H⋯O hydrogen bonds, forming chains parallel to the b axis.

3-(2,4-Dichloro-benzyl-idene)-1,5-dioxa-spiro-[5.5]undecane-2,4-dione.

In the title mol-ecule, C(16)H(14)Cl(2)O(4), the 1,3-dioxane and cyclo-hexane rings exhibit distorted boat and chair conformations, respectively. In the crystal, a pair of weak inter-molecular C-H⋯O hydrogen bonds link the mol-ecules into an inversion dimer.

5,5'-[(2,4-Dichloro-phen-yl)methyl-ene]bis-(2,2-dimethyl-1,3-dioxane-4,6-dione).

The title compound, C(19)H(18)Cl(2)O(8), was prepared by the reaction of 2,2-dimethyl-1,3-dioxane-4,6-dione and 2,4-dichloro-benzaldehyde in ethanol. The two 1,3-dioxane rings exhibit boat conformations. In the crystal, mol-ecules are linked by weak inter-molecular C-H⋯O and C-H⋯Cl hydrogen bonds, forming chains parallel to the a axis.

2,2-Dimethyl-5-(2,3,4-trimeth-oxy-benzyl-idene)-1,3-dioxane-4,6-dione.

The title compound, C(16)H(18)O(7), was prepared by the reaction of 2,2-dimethyl-1,3-dioxane-4,6-dione and 2,3,4-trimeth-oxy-benzaldehyde. The 1,3-dioxane ring is in a slightly distorted boat conformation. The crystal structure is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

5-(4-Hy-droxy-benzyl-idene)-2,2-dimethyl-1,3-dioxane-4,6-dione.

The title compound, C(13)H(12)O(5), was prepared by the reaction of 2,2-dimethyl-1,3-dioxane-4,6-dione and 4-hy-droxy-benz-alde-hyde in ethanol. The 1,3-dioxane ring is in a distorted boat conformation. In the crystal, inversion dimers linked by pairs of O-H⋯O hydrogen bonds generate R(2) (2)(20) rings.

5-(4-Fluoro-benzyl-idene)-2,2-dimethyl-1,3-dioxane-4,6-dione.

The title compound, C(13)H(11)FO(4), was prepared by the reaction of 2,2-dimethyl-1,3-dioxane-4,6-dione and 4-fluoro-benz-alde-hyde in ethanol. The 1,3-dioxane ring adopts an envelope conformation. The crystal structure is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

(E)-2,2-Dimethyl-5-(3-phenyl-allyl-idene)-1,3-dioxane-4,6-dione.

The title compound, C(15)H(14)O(4), was prepared by the reaction of 2,2-dimethyl-1,3-dioxane-4,6-dione and (Z)-3-phenyl-acryl-aldehyde in ethanol. The dioxane ring is in a sofa conformation with the C atom bonded to the two methyl groups forming the flap. With the exception of the flap atom and the methyl group C atoms, all other non-H atoms are essentially planar, with an r.m.s. deviation of 0.067 (1) Å. The crystal structure is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

3-(4-Meth-oxy-benzyl-idene)-1,5-dioxa-spiro-[5.5]undecane-2,4-dione.

In the title mol-ecule, C(17)H(18)O(5), which was prepared by the reaction of (R)-1,5-dioxaspiro-[5.5]undecane-2,4-dione and 4-meth-oxy-benzaldehyde with ethanol, the 1,3-dioxane ring is in a distorted envelope conformation with the spiro C atom forming the flap. The crystal structure is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

2-(1H-Benzotriazol-1-yl)-1-(4-ethyl-benzo-yl)ethyl 2-chloro-benzoate.

In the crystal structure of the title compound, C(24)H(20)ClN(3)O(3), weak inter-molecular C-H⋯O hydrogen bonds link the mol-ecules into chains extended along the a axis. The crystal studied was found to be an inversion twin.

5-(2-Fluoro-benzyl-idene)-2,2-dimethyl-1,3-dioxane-4,6-dione.

The title compound, C(13)H(11)FO(4), was prepared by the reaction of 2,2-dimethyl-1,3-dioxane-4,6-dione and 2-fluoro-benzaldehyde in ethanol. In the crystal structure, mol-ecules are linked into chains by weak inter-molecular C-H⋯O hydrogen bonds.

3-(2-Furylmethyl-ene)-1,5-dioxaspiro-[5.5]undecane-2,4-dione.

In the title mol-ecule, C(14)H(14)O(5), the 1,3-dioxane ring is in an envelope conformation with the ring C atom common to the cyclo-hexane ring forming the flap. The other five atoms of the 1,3-dioxane ring are essentially planar [maximum deviation from the least-squares plane = 0.041 (3) Å] and form a dihedral angle of 13.75 (2)° with the furan ring. In the crystal structure, weak inter-molecular C-H⋯O hydrogen bonds form extended chains along [101].