LEAD SELENIDE CAPPED WITH A BENZOATE LIGAND

Abstract

Semiconductor materials offer several potential benefits as active elements in the development of harvesting-energy conversion technologies. In particular, lead selenide (PbSe) semiconductors have been used and proposed to design solar energy harvesting devices, IR sensors, FET devices, amongst others. The present disclosure provides a lead selenide capped with an aromatic ligand. The use of an aromatic ligand, and more specifically benzoic acid, provides robustness and more durability to the lead selenide, and therefore prevents the lead selenide from breaking or cracking easily. Also the aromatic ligand prevents the degradation and oxidation of the lead selenide, without affecting any of the lead selenide electronic and chemical characteristics.

Claims

1. A lead selenide capped with an aromatic ligand comprising a particle of lead selenide and an aromatic ligand capped to said lead selenide.

2. The lead selenide capped with an aromatic ligand according to claim 1, wherein the aromatic ligand is benzoic acid.

3. The lead selenide capped with an aromatic ligand according to claim 1, wherein the aromatic ligand is 4-vinylbenzoic acid.

4. The lead selenide capped with an aromatic ligand according to claim 1, wherein the aromatic ligand is 3-vinylbenzoic acid.

5. The lead selenide capped with an aromatic ligand according to claim 1, wherein the aromatic ligand is 1-pyrenecarboxylic acid.

6. A lead selenide capped with an aromatic ligand comprising a particle of lead selenide and an aromatic ligand capped to said lead selenide, whereby the lead selenide's electrochemical behavior occurs in negative potentials.

7. The lead selenide capped with an aromatic ligand according to claim 6, wherein the aromatic ligand is benzoic acid.

8. The lead selenide capped with an aromatic ligand according to claim 6, wherein the aromatic ligand is 4-vinylbenzoic acid.

9. The lead selenide capped with an aromatic ligand according to claim 6, wherein the aromatic ligand is 3-vinylbenzoic acid.

10. The lead selenide capped with an aromatic ligand according to claim 6, wherein the aromatic ligand is 1-pyrenecarboxylic acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated herein, constitute part of the specification and illustrate the preferred embodiment of the disclosure.

[0027] FIG. 1 shows the chemical structure of oleic acid (left) and benzoic acid (right).

[0028] FIG. 2 shows a comparison of X-ray powder diffractograms (XRPD) between PbSe particles with benzoic acid ligands synthesized at 100 C., 150 C. and 250 C. XRPD of PbSe with oleic acid ligand and benzoic acid are also shown for comparison in accordance with the principles of the present disclosure.

[0029] FIG. 3 shows an IR spectra of benzoic acid and of PbSe with benzoic acid as the capping ligand in accordance with the principles of the present disclosure.

[0030] FIG. 4 shows a secondary electron detector SEM micrographs of PbSe with benzoic acid ligand at a) 100 C., b) 150 C. and c) 250 C. on a carbon tape substrate in accordance with the principles of the present disclosure.

[0031] FIG. 5 shows an NIR absorption spectra of synthesized PbSe with benzoic acid at 100 C., 150 C. and 250 C. in accordance with the principles of the present disclosure.

[0032] FIG. 6 shows a Cyclic voltammograms of PbSe with benzoic acid ligand on a glassy carbon electrode surface. At the left, the cyclic rate was 25 mV/s and at the right, the cyclic rate was 100 mV/s in accordance with the principles of the present disclosure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] Lead acetate (reagent grade) and toluene (reagent grade) were obtained from Fisher Scientific. On the other hand, the elemental selenium (99.999% pure), 1-octadecene, benzoic acid, and trioctylphosphine were obtained from Sigma-Aldrich.

[0034] The synthesis of PbSe with benzoic acid as a capping ligand is carried at about 200 C. temperature, preferably at 250 C., via nucleation (bottom-up method) in an opened environment comprising the following steps:

[0035] Step 1: In a round bottom flask stoichiometric amounts of lead acetate, preferably 3.795 grams, and recrystallized benzoic acid, preferably 1.8349 grams, are added to 40 mL of a 50:50 mixture of toluene and 1-octadecene in an opened environment. This reaction mixture is heated at about 200 C. temperature, preferably at 250 C., and maintained at constant stirring for about one hour. This generates a lead benzoate solution.

[0036] Step 2: In another round bottom flask an stoichiometric amount of selenium powder with respect to the lead acetate of Step 1, preferably 0.0690 grams, and 1.6 mL of tri-octylphosphine is added to 40 mL of 1-octadecene and heated at about 200 C. temperature, preferably at 250 C., at constant stirring in an opened environment for about 20 to 30 minutes. This generates a selenide solution.

[0037] Step 3: Adding five milliliters (5 mL) of the lead benzoate solution of Step 1 into the selenide solution of Step 2 at a rate of 1 mL per 30 seconds. This generates a lead selenide with benzoic ligand and a byproduct.

[0038] Step 4: When the addition of Step 3 is completed, the byproduct is decanted and the lead selenide with benzoic ligand is centrifuged for 15 minutes with ethanol.

[0039] Step 5: The ethanol is decanted and the lead selenide with benzoic ligand were re-suspended in hexane at room temperature.

[0040] Characterization

[0041] A lead selenide containing aromatic ligand is provided in the present disclosure, and more particularly, a lead selenide containing benzoic acid as the capped ligand.

[0042] Also, a simple, low cost, opened environment method for synthesizing PbSe particles using benzoic acid as the capping ligand has been provided according to the principles of the present invention.

[0043] The lead selenide of the present disclosure were compared with PbSe using oleic acid as the capping ligand.

[0044] In FIG. 2, we can observe that the diffraction pattern of lead selenide with benzoic acid prepared at 100 C. and 150 C. are very different from the diffraction pattern of PbSe with oleic acid. However, only the synthesis of PbSe with benzoic acid prepared at 250 C. temperature resembles the crystal structure of PbSe oleic acid.

[0045] FIG. 3 shows the IR spectra of benzoic acid as well as for the PbSe with benzoic acid as the capping ligand. The IR spectrum of benzoic acid shows the acidic OH stretch at 3071 cm.sup.1 and the CO stretch at 1670 cm.sup.1. Other bands are also present which are characteristic of this aromatic carboxylic acid compound. However, is very interesting that upon complexation of benzoic acid with PbSe (particularly with Pb.sup.+2), the IR spectrum shows that the OH stretch at 3071 cm.sup.1 is not present. This indicates complete complexation between the carboxylate group with the PbSe particle. To corroborate this finding, we also observed that the intensity of CO stretching peak at 1670 cm.sup.1 was dramatically reduced, while the peak of the aromatic CC vibrational stretch is present around 1500 cm.sup.1.

[0046] FIG. 4 shows secondary electron detector SEM micrographs of PbSe with benzoic acid prepared at 100 C., 150 C. and 250 C. As can be observed in FIG. 4, the synthesis of PbSe with benzoic acid at 100 C. produces particles that have more like a laminar structure rather than crystals. When the temperature was increased during the synthesis, some agglomeration is observed. However, at 250 C. particles are present showing a spherical shape. The mean size of PbSe particles with benzoic acid prepared at 250 C. is around 500 nm as determined by SEM, which corroborates our previous results obtained in our XRPD studies (FIG. 2).

[0047] FIG. 5 shows that PbSe with benzoic acid retained their electronic properties. PbSe with benzoic acid have a max around 1403 and 1630 nm, which are in agreement with previous results using oleic acid as the capping ligand.

[0048] Electrochemical Studies

[0049] A 500 L of PbSe with benzoic acid solution (concentration of the sample=2 mg/mL) were drop-casted into the surface of a glassy carbon electrode. FIG. 6 shows the cyclic voltammograms for the electrochemical reduction process of benzoic acid at 25 mV and at 100 mV/s. The particles are electrochemically active in the region where Pb(II) reduces to metallic lead. This electrochemical process usually occurs in positive potentials. Due to the presence of aromatic ligands, and more specifically, benzoic acid, the electrochemical behavior of the PbSe of the present disclosure occurs in negative potentials. This result indicates that PbSe with benzoic acid is resistant to air and water oxidation.

[0050] Due to similar characteristics with benzoic acid, there are several ligands that can be used to synthesize robust and more durable lead selenide in an opened environment in accordance to the present invention. There are several commercially available aromatic ligand exchangers that can be employed for the attachment to a quantum dot core. They have a component that can be used for polymerization. Ligands such as 4-vinylbenzoic acid, 3-vinylbenzoic acid, which have a vinyl group have been known to produce films using electropolymerization at an electrode surface. Also 1-pyrenecarboxylic acid can be used as the capping ligand in accordance to the principles of the present invention.