Want guidance for choose best UART or USART RF module for Arduino

hello every body , I want to create a Star or Mesh network with arduino like image below :

the distance node between master is about 2 km.

I want to create full duplex communication , send sensor information from nodes to master node , that master node reply to each one.

witch kind of RF module is best for my solution ? 

my RF module must be UART or USART , Cause of I cant use SPI Protocol , because I use SD card that use SPI Protocol.

Many RF modules use a serial port for coms between the module and the host processor, it will likely be other considerations that dictate the module to use.
What data band width per channel do you need, and remember that the network controller needs to be able to manage the total bandwidth of the star network.
The range at 2Km is far too much for many of the modules, even with a high gain whip antenna, so you are talking about directional antenna, Yagi or cantenna, for example, and/or bi-directional power amplifiers. You are probably stuck with using the 2.4GHz ISM band, since that is where the majority of the licensed radio modules operate, but there are restrictions on radiated power obviously.
As I indicated earlier, if your band width is very low, then have a look at LoRa WAN, it is designed for low band width long range (up to 10Km) star networks,
cheers,
Richard

yes my band width is low , so you comment me to use LoRa WAN , Tanks a lot .