Synthesis method of g-C3N4/c composite material based on hollyhock stalk

Abstract

The present disclosure provides a synthesis method of a g-C.sub.3N.sub.4/C composite material based on a hollyhock stalk, including the following steps: (1) pretreatment of hollyhock stalks; and (2) fabrication of the g-C.sub.3N.sub.4/C composite material. In this method, with the hollyhock stalk as a carbon skeleton, g-C.sub.3N.sub.4 is spread on a template surface to form a laminated layer, and a composite system with a special structure is constructed. Compared with pure phase g-C.sub.3N.sub.4, the composite material substantially increases specific surface area and has a clear interface; the carbon skeleton not only functions as a rigid support, but also increases the electron transfer efficiency of the composite material, thereby improving the separation efficiency of photogenerated carriers and the utilization rate of visible light. Raw materials used in the method are inexpensive and environmentally friendly, which can be used for industrial production and bulk production of eco-friendly materials for harnessing environmental organic pollutants.

Claims

1. A synthesis method of a g-C.sub.3N.sub.4/C composite material based on a hollyhock stalk, comprising the following steps: step 1, pretreatment of hollyhock stalks cutting freshly picked hollyhock stalks into segments, washing stalk segments with deionized water, and soaking the stalk segments in a pretreatment solution to remove chlorophyll and bioactive substances therein; after soaking, washing the stalks with deionized water and drying naturally, avoiding direct sunlight, and collecting dried stalks for later use; step 2, fabrication of the g-C.sub.3N.sub.4/C composite material using dicyandiamide as a precursor to prepare an impregnation solution, impregnating the stalks pretreated in step 1 in the impregnation solution for treatment, and conducting dehydration and heat treatment to generate the g-C.sub.3N.sub.4/C composite material, wherein the hollyhock stalks and the dicyandiamide have a mass ratio of (1:1)-(1:4).

2. The synthesis method according to claim 1, wherein the stalk segments in step 1 are 3-5 cm in length.

3. The synthesis method according to claim 1, wherein the pretreatment solution in step 1 is a mixture of water and ethanol in a volume ratio of (1:1)-(1:2) and the pretreatment solution is adjusted to a pH of 2-3 with 0.1 mol/L dilute hydrochloric acid; soaking time is 3-4 weeks; after soaking, the stalks are washed until a pH value of a washing solution is neutral prior to air-drying.

4. The synthesis method according to claim 1, wherein the stalks pretreated in step 2 are stirred in the impregnation solution in a 50° C. water bath for 1-2 h, stirring is stopped after the precursor is completely dissolved, and the stalks are kept holding in the water bath for 20-24 h and dried at 60-80° C. overnight.

5. The synthesis method according to claim 1, wherein the heat treatment in step 2 is conducted in a muffle furnace, and reaction conditions are as follows: heating to 500-550° C. at 3-5° C./min in an air atmosphere and holding for 4-6 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an X-ray diffraction (XRD) pattern of a g-C.sub.3N.sub.4/C composite material;

(2) FIG. 2 is a scanning electron micrograph (SEM image) of a g-C.sub.3N.sub.4/C composite material;

(3) FIG. 3 is a transmission electron micrograph (TEM image) of a g-C.sub.3N.sub.4/C composite material;

(4) FIG. 4 is a curve chart of the visible light degradation of Rhodamine B (RhB) for different samples;

(5) FIG. 5(a) is a curve chart of the degradation of RhB dye by a g-C.sub.3N.sub.4/C composite material for 4 cycles; (b) is an XRD pattern of the g-C.sub.3N.sub.4/C composite material before and after the cyclic photocatalysis experiment;

(6) FIG. 6 illustrates the principle of the photocatalysis of a g-C.sub.3N.sub.4/C composite material.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) The present disclosure will be further described in detail and completely below in conjunction with the examples, but does not limit the content of the present disclosure.

Example 1

(8) (1) Washed hollyhock stalks were cut into segments (3 cm), soaked in a pretreatment solution (the volume ratio of water to ethanol was 1:1, the solution was adjusted to pH 2 with 0.1 mol/L dilute hydrochloric acid, and the soaking time was 3-4 weeks) to remove chlorophyll and bioactive substances therein; after soaking, the stalks were washed with deionized water and dried naturally, direct sunlight was avoided, and dried stalks were collected for later use; (2) 1.5 g of pretreated dry hollyhock stalks and 3 g of dicyandiamide were dissolved in 50 mL of deionized water, and stirred in a 50° C. water bath for 1 h; stirring was stopped until the dicyandiamide was completely dissolved; the mixture was held in the 50° C. water bath for 24 h, transferred to an alumina crucible and dried at 60° C. overnight; (3) the resulting solid was placed in a muffle furnace, heated to 550° C. at 3° C./min in an air atmosphere and held for 4 h, calcinated and then ground to obtain a g-C.sub.3N.sub.4/C composite material.

(9) FIG. 1 is an XRD pattern of the g-C.sub.3N.sub.4/C composite material. It can be seen from the figure that the g-C.sub.3N.sub.4 phase (002) is more obvious, the peak shape is sharp, and the C phase (001) is not obvious. The main reason is that the C phase is mainly amorphous and the crystallization peak is not obvious. In FIG. 2, the carbon skeleton structure of the hollyhock stalk template and the g-C.sub.3N.sub.4 sheets supported on the surface of the template can be clearly seen in the SEM image, and the TEM image of FIG. 3 shows that the g-C.sub.3N.sub.4 sheet has a porous structure, with a large specific surface area, which can effectively promote the binding of organic dyes to chemical reactive sites on the surface of the photocatalytic material, and improve its photocatalytic degradation efficiency.

(10) 30 mg of the product was added to 100 mL of 20 mg/L Rhodamine B solution, samples were taken every 20 min under the xenon lamp simulated visible light irradiation, a UV-Vis spectrophotometer was used to analyze its concentration change in combination with the standard curve, and a photocatalytic degradation efficiency curve was plotted. As shown in FIG. 4, its degradation rate reaches 53.91% at 120 min after illumination. The cyclic experiment results in FIG. 5 show that the photocatalytic activity of the g-C.sub.3N.sub.4/C composite material decreases insignificantly after four cycles of the catalytic degradation, and there is no significant difference between the XRD patterns of the catalysts before and after the catalytic reaction.

(11) The photocatalytic mechanism diagram (FIG. 6) shows that in the g-C.sub.3N.sub.4 photocatalytic material, the carbon skeleton formed by the calcination of hollyhock stalk acts as an electron transfer mediator that provides an electron transfer channel for photogenerated carriers, thereby reducing the recombination efficiency of photo-induced electrons and photogenerated holes and improving the efficiency of photocatalytic degradation of organic dyes in the system. Meanwhile, the carbon skeleton further provides a rigid support for the microscopic morphology of the material, so that it can maintain a high specific surface area. Thus, there are more active sites for chemical reactions, and the photocatalytic degradation efficiency is further improved.

Example 2

(12) (1) Washed hollyhock stalks were cut into segments (5 cm), soaked in a pretreatment solution (the volume ratio of water to ethanol was 1:2, the solution was adjusted to pH 2 with 0.1 mol/L dilute hydrochloric acid, and the soaking time was 3-4 weeks) to remove chlorophyll and bioactive substances therein; after soaking, the stalks were washed with deionized water and dried naturally, direct sunlight was avoided, and dried stalks were collected for later use; (2) 1.5 g of pretreated dry hollyhock stalks and 1.5 g of dicyandiamide were dissolved in 50 mL of deionized water, and stirred in a 50° C. water bath for 1 h; stirring was stopped until the dicyandiamide was completely dissolved; the mixture was held in the 50° C. water bath for 24 h, transferred to an alumina crucible and dried at 80° C. overnight; (3) the resulting solid was placed in a muffle furnace, heated to 520° C. at 4° C./min in an air atmosphere and held for 6 h, calcinated and then ground to obtain a g-C.sub.3N.sub.4/C composite material.

Example 3

(13) (1) Washed hollyhock stalks were cut into segments (4 cm), soaked in a pretreatment solution (the volume ratio of water to ethanol was 1:2, the solution was adjusted to pH 3 with 0.1 mol/L dilute hydrochloric acid, and the soaking time was 3-4 weeks) to remove chlorophyll and bioactive substances therein; after soaking, the stalks were washed with deionized water and dried naturally, direct sunlight was avoided, and dried stalks were collected for later use; (2) 1.5 g of pretreated dry hollyhock stalks and 6.0 g of dicyandiamide were dissolved in 50 mL of deionized water, and stirred in a 50° C. water bath for 1 h; stirring was stopped until the dicyandiamide was completely dissolved; the mixture was held in the 50° C. water bath for 24 h, transferred to an alumina crucible and dried at 60° C. overnight; (3) the resulting solid was placed in a muffle furnace, heated to 500° C. at 5° C./min in an air atmosphere and held for 6 h, calcinated and then ground to obtain a g-C.sub.3N.sub.4/C composite material.