ESP8266 freeze over time

Here is my code.

/*
Labo Sensors
Connected to Huzzah ESP8266

Contains theses sensors:
-Temperature and humidity
  
*/

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include "DHT.h"

// DHT22 Temperature sensor settings
#define DHTPIN 2     // what digital pin we're connected to temperature sensor
#define DHTTYPE DHT22   // DHT 22  (AM2302), AM2321

// Initialize DHT sensor.

DHT dht(DHTPIN, DHTTYPE);

// Light Sensor
const int light = 4; // Sensor is connected to ESP8266 pin #4
int lightState = 0; // Reset the light sensor
char* lightOnOff[]={"OFF","ON"};

// Water leak sensor
const int flood = 12; // the flood sensor that is connected to pin 12
int floodState = 0; //Reset the flood detector

//Network value
const char* ssid = "Network";
const char* password ="Password";
const char* mqtt_server = "10.0.1.101";

WiFiClient espClient;
PubSubClient client(espClient);
char message_buff[50];

void setup() {
Serial.begin(115200); // Starts the serial communication
setup_wifi();
client.setServer(mqtt_server, 1883);
client.setCallback(callback);
Serial.println("DHTxx test!");
dht.begin();

}

void loop() {
  if (!client.connected()){
  reconnect();
}
client.loop();
Serial.println("");
Serial.println("Sending Value by MQTT");
sendMessage(); //Transmit by MQTT different sensors

}

//sendMessage Function
void sendMessage(){
  //Temperature and Humidity sensor
  delay(2000);
  float h = dht.readHumidity();// Humidity
  float t = dht.readTemperature();// Temperature in Celsius
  String pubString = String(t);
  pubString.toCharArray(message_buff, pubString.length()+1);
  client.publish("Boubounouche/Labo/Temperature", message_buff);
  pubString = String(h);
  pubString.toCharArray(message_buff, pubString.length()+1);
  client.publish("Boubounouche/Labo/Humidity", message_buff);  

  //Publishing Light Sensor
  lightState = digitalRead(light);
  Serial.print(F("\nSending light sensor val "));
  Serial.println(lightOnOff[lightState]);
  pubString = String(lightOnOff[lightState]);
  pubString.toCharArray(message_buff, pubString.length()+1);
  client.publish("Boubounouche/Labo/LightSensor", message_buff);

  // Publishing Flood detector hot water tank
  floodState = digitalRead(flood);
  Serial.println(floodState);
  pubString = String(floodState);
  pubString.toCharArray(message_buff, pubString.length()+1);
  client.publish("Boubounouche/Labo/Flood", message_buff); 
  
  delay(8000);
}

// Establishing connection to Wifi
void setup_wifi(){
 delay(10);
 Serial.println();
 Serial.print("Connecting to ");
 Serial.println(ssid);

 WiFi.begin(ssid, password);

 while (WiFi.status() != WL_CONNECTED){
  delay(500);
  Serial.print(".");
 }

 Serial.println("");
 Serial.println("WiFi Connected");
 Serial.println("IP address: ");
 Serial.println(WiFi.localIP());
}
void callback(char* topic, byte* payload, unsigned int length) {
}

void reconnect(){
//Loop until we're reconnected
while (!client.connected()){
  Serial.println("");
  Serial.print("Attempting MQTT connection...");
  //Attempe to reconnect
  if (client.connect("ESP8266Client")){
    Serial.println("connected");
    
  }
  else{
    Serial.print("failed reconnection");
    Serial.print(client.state());
    Serial.println("try again in 5 seconds");
    //Wait 5 seconds before retrying
    delay(5000);
    }
  }
}